Well, firstly it was through a letting agent and they are cunts about it. First of all they checked with the landlord to see if he was happy to surrender the tenancy (which presumably he could have said no to). Then I paid a ‘surrender fee’ of 1 month’s rent + VAT…when I asked what that was they said it was for the costs of remarketing and all that sort of thing. Basically a load of shit but they see an opportunity to get some cash. Then I was responsible for any rent until they had re-let it. Got really close to my leaving date but they did manage to re-let in the end so I ended up only being responsible for about 2.5 weeks rent, but bear in mind that you’re paying rent on a new place by then.
tl;dr - I basically paid around 2 months rent for it once you add the VAT. Not all agents have a surrender fee so it’s important to check the terms of your contract I guess.