You can get into lots of trouble for no MOT but as long as you are taxed and have no accidents and don't go past one of those number plate recognition road checks, I'm not sure how anyone would know (yes, I know it is all computerised now but does anyone actually chase people with an expired MOT? Apologies if they do).
As Ratter says, even if you only have 1 day left on your MOT, you can still tax your car - so tax it now before the MOT runs out.
Better still, get an MOT!!!!