For the final semester exchange, I chose London as my first hand choice since I had dreamed of living there since I was a teen. I applied to Imperial College because of its good reputation as a school and because they seemed to have interesting research within the field of immunology. 
I was very happy  to be accepted to the school, but surprised when I wrote to principal investigators of labs I wanted to do projects in, but didn't get any answers. It was not very clear to me that we were only allowed to do projects in a limited selection of departments and also that we were not supposed to make contact with the PIs ourselves, only through the Imperial coordinator. Also the coordinator at Imperial was at times very difficult to get a hold of. It all worked itself out in the end,  but that would've been good to know from the start.
Also good to know which I didn't, was that if you are really interested in a certain department that isn't available to you, you could nag the coordinator a bit and he will try to pull some strings. 

My supervisor wished for me to start on the 16th of January, when a course he was professor of and that also concerned the basics of my project, started. The final day of my last course at KI was just the day before that, and I arranged for an early presentation of the last work and then took the flight to London in the afternoon. It would've been nice to have a few extra days in London before starting the project to have a look around, get settled and find the university. But arriving the night before and then getting up early the next day was fine (especially because they're an hour behind us, so you kind of get an extra hour of sleep anyhow). Imperial College has a couple of campuses and mine was in South Kensington, close to Hyde Park and the national history museum, so it was extremely easy to get to and there were signs everywhere telling you how to get to Imperial College.
It's also a good idea to have downloaded some maps from the college website over what the buildings are called and where you are going, as that is the most difficult part. 
But once I was in the right place, I was chaperoned everywhere, so I didn't have to think at all about where to find the lab or lunch or the gym or how to get my key, which was nice. Also I was advised to join the Imperial College Erasmus Club on Facebook, which I did. They organized some things and everyone was welcome, also the KI people at Kings College and other occasional non-Imperial people. I was also on some sort of mailing list which I think was also the Erasmus group which offered me discounted trips to interesting places around England, such as Stonehenge, Bath and Oxford. 

London is so expensive, it makes Stockholm look cheap. 
Yes, their alcohol may be cheaper. In certain places only marginally. The biggest mistake is thinking 1 pound is approximately 10 kronors. This will ruin you. It's more, and it fluctuates and every time you get money out of a machine it costs you money as well. I wish I would've done more "cashback" whenever I visited a big supermarket instead. In some supermarkets, most likely the big ones, you can ask for "cashback" and add a sum to what you are buying, and then you'll get cash back for the extra amount. Pretty straight forward. 
I had a fixed rent at 610 pounds/month (that is considered a good deal in London by the way) and the public transport card was 100 pounds/month from zone 3 where we were living. That was already all the money I was getting from CSN. But with stipends and a little extra cash I had coming in per month, I had calculated that I would still have an extra 400 pounds to spend/month. That was nowhere near enough and I had to eat into my entire savings. 
So the big question - did I go wild and crazy and just throw money around me like it was nothing? The answer is no. 
I bought a bike (+helmet +lock) to a combined cost of 80 pounds and so I could save on public transport costs by cycling to zone 2. Buses are always free if you have a zone card so if I didn't feel like cycling I could take the bus to zone 2. The last weeks I cycled all the way to work (which I wish I would've done earlier, it was only 10 km and a very nice route!) so then I only had the "pay as you go" oyster card. BEWARE IF YOU CYCLE. It is VERY dangerous in London. Never assume that anybody sees you and don't take any chances. Get used to the left hand traffic before you enter big roads.
I sold the bike, helmet and lock on gumtree.co.uk at the end of the semester for 70 pounds, so I hardly lost any money on it. I think the biggest money-thief was the food. Healthy food is very hard to come by in London and when you do come by it, it's expensive. But then all the little things add up as well. It's hard to explain, but without acting very different from my life in Stockholm, I spent twice the amount of money. So, have savings and prioritize and do what you can to reduce your costs. Living on walking/cycling distance to your campus can save you a lot of money.  

Me and Lina from KI had already talked about living together if possible when going to London. We had some tips to look on gumtree.co.uk , ask the college about housing, and also a site called sparerooms.co.uk, the latter being my favourite since you could put in price range and neighborhood that you were interested in. 
It was actually hard to find a place where they didn't want you to be able to move in right away, and so I think it's fine to start looking quite close to arrival. One of the guys just lived at a hostel the first days, then had an agency put him in a house, then switched to the school housing. Me and Lina got offered a place by a friend of Lina and so we didn't have to care about that stuff at all in the end. It was a nice place that we had to ourselves, but it was very expensive (610 pounds/person, considered a good deal, as mentioned) and considered quite far away from the center. I think it would've been possible to get a place at campus or in zone 1 for the same price, but then with only a room and sharing with a lot of other people so I guess it was a pretty good deal.
We did however have some issues with our landlord that we managed to resolve, but a good tip no matter who your landlord is, even if it's a friend, always take pictures of how it looks in the apartment on the day you arrive, and make sure to document possible pre-existing damages or if the place is really dirty or broken things.  

So my study was my project work. I also sat in on lectures of a course that my supervisor was the professor of and wanted me to take. I did however not do any of the course extra-work or exams as I was assigned and wanted to do the 30 hp project and not the 22.5 hp + 7.5 hp course work one.
But it was very good to sit in on the lectures as I had chosen (as much as I could choose, since as mentioned previously I didn't have that many choices) a project in a field that I knew hardly anything about. As happy as I am to have broadened my knowledge and learned new skills, in retrospect it was not my best choice. Since I hardly knew anything about it, it wasn't all that relevant to my KI studies, or to anything I would like to do in the future. More than anything it was a very educative experience in what I never want to work with ever again. Unfortunately I did not get a good relationship with my supervisor no matter how hard I tried, but fortunately it was not only me he hated but in fact, everyone. So I had a very good relationship with my lab-mates as we took turns in being the undesirable of the day. My point being - if possible, try to contact the people who work for your supervisor and ask beforehand what it is like to work for him or her.
However, in consistency with my own personal experience, I've also heard a lot of stories from people saying that hierarchy is very strict in England. You do not discuss with the boss and as a bachelor student, your thoughts or ideas are not interesting. The boss tells you what to do and you do it and ask nothing. From KI and other placements, I am used to being able to speak with my supervisors, that asking questions is encouraged and having own ideas is appreciated. So this was a difficult difference for me, but at the same time I evolved my independence a bit so it wasn't all negative.      

One of the great advantages of going to London is that everybody speaks English. But of course, since English is the native language, there is more dialect, some people speak faster and less articulate and use slang words you've never heard. Another fascinating thing about London is that it is truly a melting pot of people from all over the world. Being a foreigner in London probably made me part of the majority rather than the minority. There is respect and interest for other peoples cultures and traditions and you can find food from all over the world in the city. It is also true that politeness is very important in London. If your backpack accidentally touches someones knee in the midst of rush hour and you're not deeply apologetic about it, people will get the evil eye. In fact, you might get angry stares just for bringing a backpack. However, rush hour in London is true horror. Especially for someone like me who is slightly claustrophobic. Again I give you my tip on living walking or biking-distances to campus!
That there is a big pub-culture in London does not come as a shock to anyone I think. One very nice aspect of London pubing is that it isn't all about drinking. There are many Muslims in London who don't drink because of religious beliefs. But everyone comes to the pub and nobody thinks it's strange if you order a cola instead of a beer or wine. It's a very friendly environment and people of all ages come there to chat and be part of society. My biggest shock with the pubs was that they close at eleven p.m.!

As I mentioned before, there was an Erasmus Club at Imperial that arranged events every now and then. As I understood it, it was really a question of how engaged the Imperial students running the group were. During some of the previous years, there had apparently not been much going on. Still it's a good idea to join the facebook group and write that you are new to the city and ask if somebody is up for anything. Most exchange students find themselves in the same situation and are very willing to meet and invite new people to whatever they have planned.
At Imperial College there is also a school gym called Ethos which is free (!) for students. A one-time fee of 40£ is however applied for an introduction to the gym, which is mandatory. At Ethos there's a pool in the basement, courts for tennis, squash, volleyball etc., a climbing wall, classes every day and a small gym with cardio-equipment, some machines and some free weights. There's also lots of clubs to join through the union (not free), so there's a lot of ways to work out and meet people through sports at Imperial. Of course it's also situated right next to Hyde Park where there's plenty of space for running and there's plenty of races held there as well.
Whatever you can't find at Imperial College, you can definitely find somewhere in the rest of London. Pretty much everything exists there. The two most annoying aspects are 1. London is SO huge. It can take hours to get around. And it'll be crowded. 2. It's so expensive. I constantly had to worry about how much was I spending here or there and give up quite a few things to make it through the month.
As a student, walking through the shops of Oxford Street was just one big tease. Although clothes are cheaper in London, there's also so much more to buy... Cheap and one of the best experiences of London was (at least for me) Brick Lane market. Lots of interesting people to watch, food from all over the world for 3£ and vintage clothing in all price ranges. Also some fantastic pubs and clubs are in the area.
Be aware though - even most clubs in London close incredibly early (around 1 a.m.) and all the public transport except buses stops going about half an hour earlier. Well, I couldn't exactly afford lots of club-nights anyway, so it didn't really matter too much to me in the end.   

This was my second time abroad with KI exchange programs. It gave me the opportunity to go to London which I've always dreamed of. Going abroad is always a very valuable experience in that you get to know so many different kinds of people, you broaden your views of what life could be and you get a deeper understanding for other people and cultures.
The more you are abroad, the more you understand about people, work life and what you want out of life.
The first exchange to Leiden university was eye-opening in another way than the second, and I'm happy we had the opportunity to do one semester of university life at another country, and one with work life.
 The connections you make, experiences and insights you gain and stories to tell will definitely be beneficial to your future career.