The government budget announcement used the following wording ...

Following the expiry of the UKs derogations from the Energy Products Directive on 31 December 2006, from 1 November 2008 fuel used for the purposes of private pleasure flying and private pleasure boating will no longer benefit from the current reduced and exempt rates of duty.

Note they say "used" not "bought". I think its still highly unclear what the situation will be regarding fuel bought before the cut-off but used after.