HM Treasury does not make estimates for pre-financing. The amounts of pre-financing are recorded in the annual accounts of the European Communities, which are then reported on by the European Court of Auditors.
The latest figures available for pre-financing and recovery orders are for the 2005 financial year and may be found in the 'Final Annual Accounts of the European Communities 2005' at
http://ec.europa.eu/budget/library/publications/fin_manag_account/fin_annual_ acc_2005_en.pdf