I feel your pain - my logbook was stolen in 2005.
The CAA used to cover this in a FAQ, but I can't find it on their website any longer. The relevant wording was:
Originally Posted by CAA
Individuals who have lost a logbook and are intending to obtain further licences will be required to obtain a Sworn Affidavit, completed through a solicitor or Commissioner of Oaths, detailing their flying hours to the best of their knowledge. The flying hours should be completed into categories in conjunction with the applicable licence requirements. Please refer to Section A, Page 35 of LASORS as appropriate. This is required in order for us to be able to confirm flying experience, when a further licence is applied for. Individuals who do not intend to obtain any further licence (i.e ATPL holders) are not required to obtain a Sworn Affidavit, but may wish to start a new logbook.
Edit: See
LASORS 2008 Section A p26, where the above words appear.