Well I e-mailed them and asked wether it was fine if I don't do the direct debit mandate before I get there, as I will not have a UK bank account before I do, and they said I could do it when I get there. I've payed the £100, and the next payment isn't until November. Hmm.., I do hope they will let me in, I do not wan't to sleep under a tree, and I know I am not the only person who won't have an account before moving in, so I guess they are used to it and have pretty much figured out the deal.