FCO states
A UK passport remains the property of Her Majesty’s Government in the United Kingdom and may be withdrawn at any time.
It should not be tampered with and should not be allowed to pass into the possession of an unauthorised person.
Tampering with a passport constitutes a criminal offence and renders it invalid for use.
Any case of loss or destruction should be reported immediately to the local police.
When overseas please report the theft of your passport to the local police and then the nearest British diplomatic mission.
All non-theft related passport queries should be referred directly to the British diplomatic mission.

I'm sure destruction by a third party would be seen as tampering.
Complain to the FCO and see what happens.
(porkylips looks better as the sun goes down., Mon 11 Apr 2011, 18:23, Reply)