I had a bit of a mental mix up a couple of years ago and drove a car for about 5 months without an MOT. I had it in my head it was due in Feburary, tax wasn't due till later in the year - so didn't think about it.
Anyhow, long story short - I realised - immediately went ringing out garages to find one that had a space that day, and got it done.
As luck would have it, the very next day I got pulled over on the motorway by an ANPR equipped police car. And fortunately, I had the valid MOT certificate still in the car from the day before. Phew!
I should have bought some scratch cards as well.