@Fraser
Postal votes have to be applied for several weeks in advance, and once granted, can't be exchanged for "in person" votes in a hurry.
I've failed to vote in the last few elections because I've found out that I'm working late or in a different country too near to the election to apply for a postal vote.
Sods law says I'll be in the country, with a quiet day at work now I've actually got a postal vote.
Re: RON - the nearest we have in this country is a wilfully spoiled ballot. If enough people just wrote "RON" across their papers, we could make a point.