The European Commission's employees tower to more than 54,000, researchers at the Westminster think tank Open Europe claim, as cited by Daily Telegraph.

The number is more than two times higher than official data, which sets EC staff at 25,000.

Open Europe found that the commission itself employs more than 42,000 officials, but a further 12,000 are employed at low-profile organisations such as the European Data Protection Supervisor, the Community Plant Variety Office and the European Personal Selection Agency.

Open Europe has also discovered that there are more than twice as many Brussels officials earning top salaries as there are in the British civil service. It found almost 10,000 EU officials earning more than GBP 54,000, compared with 4,640 across all Whitehall departments.

Lorraine Mullally, of Open Europe, said: "The EU discreetly publishes a Statistical Bulletin listing staff levels at its agencies, but when we contacted these agencies directly we found they had far more staff than listed."

Many of the agencies took months to answer requests. One, the European Police College, repeatedly refused to disclose its staff numbers.