Interesting question, simontrumpet!
An Electoral Commission report says there were 100,005 spoilt ballot
papers at the 2001 election.
This must be slightly lower than the true figure because five
constituencies did not supply information on spoilt papers.
The Commission's report, called "2001 general election, postal votes,
proxy votes and spoilt ballot papers", says:
"The number of spoilt ballot papers rejected at counts was 100,005,
0.38% of the total votes cast. "
"Ballot papers are rejected under the following headings:
a) Want of official mark
b) Voting for more than one candidate
c) Writing or mark by which the voter could be identified
d) Being wholly unmarked or void for uncertainty
e) Rejected in part
The information on spoilt ballot papers is incomplete, as no returns
were made from the following 5 constituencies; Manchester Gorton,
Portsmouth North, Wolverhampton North East, Wolverhampton South East
and Wolverhampton South.
Despite these gaps, there were 6,597 more ballot papers rejected on 7
June 2001 than in 1997, although the turnout was over 10% greater in
1997. A total of 0.09% more ballot papers were rejected in 2001. The
biggest single difference was in the category (d) spoilt ballots,
?Being wholly unmarked or void for uncertainty?."
There is a pdf version of the report here:
Or download it as a Word document from:
If you wanted to use the 0.38 per cent average for ballot papers
rejected across the UK to make an informed guess about how many spoilt
papers there were in the missing five constituencies, you could use
2001 constituency sizes
and 2001 turnout by constituency
Or there is a constituency by constituency report on the 2001 election
available in Excel format here:
I found these amongst Keele University's Political Science Resources:
I hope this gives you the full picture, but please let me know if
you'd like anything clarified.
Best wishes - Leli
searches on Google UK:
"rejected OR spoilt OR spoiled ballot papers" 2001