OLAF, the EU's fraud watchdog, completed a record 156 investigations into the use of Brussels' budget last year.
One quarter of the fraud probes related to Romania, which joined the 28-member bloc in 2007.
Three Eastern European countries – Hungary, Bulgaria, the Czech Republic – were the next worst offenders.
Ukip MEP Jonathan Arnott slammed the "useless" EU's financial control for allowing "tens of billions of pounds" to be lost.
He said: "This lack of control makes it much easier for fraudsters to get their sticky fingers on the money - a staggering £55million a day of which comes from the UK.
"Every day we find more and more reasons why we urgently need a referendum so we can escape the tentacles of the EU and get back our sovereignty and keep our taxpayers money in our own country."
