I realise this won't help your situation now, but it's always best to place a little sticker with the expiry date of your MOT somewhere on your dashboard. Our local garage supply us with this each time, which is very useful.
I've managed to run a car for 3 months over the MOT due date before. The garage I took it to just tutted and issued me another one covering the previous 3 months. Naughty of them, I know, but I'm sure this happens more than a few times a year. Maybe you could have a quiet word in someone's ear....