The Bank of England is responsible for collating statistics on counterfeits of its own banknotes and these are available at:
http://www.bankofengland.co.uk/banknotes/about/counterfeits.htm
Scottish and Northern Ireland banknote issuers are responsible for collating statistical information on counterfeits of their own banknote issue. The Scottish banks publish their statistics on the Committee of Scottish Clearing banks website available at:
http://www.scotbanks.org.uk/banknote_counterfeit.php
The Northern Irish banknote issuers do not publish statistics on counterfeits of their banknote issue.