I've done it.
I took the plunge and did what has been the hardest thing in my preparations for leaving from LBS - I gave notice to my company. This time of year is peak season for my company, and I was quite afraid of what their reaction would be. Despite worrying about it for weeks however, it really turned out to be a non-event.
I of course wanted to keep my relationship with my employer as friendly as possible in my final weeks and leave on good terms, but I also wanted to be compensated for my remaining paid holiday days.
So, I had the chat with my boss and and told him my intentions, and that I was very sorry for the bad timing. Instead of him being angry, he congratulated me; it didn't seem to bother him. I think he understood that it's already done - that I've made the decision and there was no way to change anything.
To smooth things over, I agreed to work until the last day possible, the day before I leave for London. It's really no problem as the only thing I need to do is pack my luggage, which will not take much time.
They will pay me for the paid holiday as well, so it really has been an ideal outcome. I guess what I can tell readers is that leaving your company isn't something to worry so much about, it won't be as bad as you think.