[SAM-S44MDS-]

Tax, MOT, insurance and new tyre's doesnt mean you haven't been drinking though does it.
Did you swerve to avoid a pothole? Object in the road? Take a corner wide?

Anything like that could make the police believe you have possibly been drinking, therefore they stopped you to check. That is their job mate. If you havent done anything wrong, then you havent got anything to worry about.

I've been stopped around 8-10 times in a few different saxo's, each time I have done nothing wrong and it was just a 'routine stop'. I had nothing to hide, car was fine. I lost around 5minutes each time, but atleast it proves they are doing their job.
So many cars out there that aint fit to be on the road., if you/friend/family got hit by one, you would be the first to say "why dont police check these cars" or something similar.
They cant win, no matter what they do somebody will always complain they are doing it wrong.

As E8_pqck said, some coppers are good people, some are dicks.