Annobel and Alison
Having been a scrutineer at a polling booth many times, i can tell you that abstention votes are noticed. Voting is compulsory here, and blank ballot papers and 'informals' ie ones where the intention is unclear, or ones full of rudeness are counted. So we ring up the booth tally saying, say, labour 500. conservative 400, informal 20. It has to all add up to the number of names crossed off the voters' list.
Scutineers are party workers watching the count to make sure nowt untoward happens. As party members they have a good look at the informals, and tell their MPs and party officials what the trend has been. Eg lots of blanks, lots of people wanting candidate X who was not standing, lots of Donald Ducks.....
BUT if you want the Tories out, vote Labour, even if you have to hold your nose to do it. Use your vote - people had to fight for it.