"Eurostat is expressing a reservation on the quality of the data reported by the United Kingdom," the European Union data agency said in releasing deficit and debt figures for the 27-state bloc.
This was due to "uncertainties" relating to when military expenditure is reported as well as funds pumped into failed lenders Bradford and Bingley and Northern Rock by the previous Labour administration under Gordon Brown.
Britain, already locked into one lengthy war in Afghanistan, is along with France the major contributor to military action against forces loyal to Libyan leader Moamer Qadhafi.
Britain "does not record military expenditure on a delivery basis, as required," Eurostat said.
The figures come days from a lavish royal wedding, also paid for by British taxpayers.
The military impact on the government deficits between 2007 and 2010 amounted to more than two billion euros. Eurostat said this takes into account Britain's spring-to-spring financial years through to the beginning of this month.
The bank bailouts account for a sum almost as large, on the same basis.