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Thank you for your replies.
Yes, there was no break clause or anything in the contract. We were hoping they might be a little more flexible as we had been tenants for such a long time (in terms of the London rental market anyway) but they wouldn't budge. We've learnt our lesson on that front and made sure the contract at our new place has a reasonable option to end the tenancy, not that we should need to hopefully.
That's a good idea to make an enquiry on the flat, I might just do that, thank you!