The European Court of Auditors said it had found irregularities affecting four per cent of total spending during 2011, equivalent to around €5.2bn (£4.17bn).
The biggest problems were in outlays on rural development, fisheries and health, the court said in its annual report, which ran to more than 240 pages.
Most errors came from the “misapplication or misunderstanding” of the EU’s complex rules, the auditor said, while a handful of cases of suspected fraud were reported.
“With Europe’s public finances under severe pressure, there remains scope to spend EU money more efficiently and in a better-targeted manner,” court president Vitor Caldeira said. “Member states must agree on better rules for how EU money is spent, and member states and the Commission must enforce them properly.”
The budget for the next seven years is currently being negotiated, with governments including the UK calling for a freeze in spending.
“It is risible that the EC wants a five per cent increase in the budget yet nearly four percent of spending is affected by error,” said Tory MEP Martin Callanan.
“Before asking for more taxpayers’ money, perhaps the commission should prioritise better spending of the money it already has.”