Tusiombe waingie Bongo Dozens of London-based Slovakians have been arrested in northern France after using Barclays bank cards to fraudulently withdraw more than £300,000 in cash. The astonishing scam saw up to 50 of the eastern Europeans arrive in Calais early last Friday morning before emptying cash points across the region. Armed police made 34 arrests, but not before many had fled with bags of money which remain unaccounted for. 'It's one of the most bizarre crimes we've ever dealt with,' said a detective working for the Judicial Police in the city of Lille. Cash machine scam: The gang were able to withdraw hundreds of thousands of euros before French police caught up with them 'These men and women had travelled across to Calais by ferry with the express intention of emptying French cash machines using Barclays bank cards issued in London. 'More than 130,000 (£114,000) was taken from the centre of Dunkirk alone in the early hours of Friday morning.' The mass withdrawals triggered alarm bells at a specialist financial monitoring unit in Paris, leading to an armed response unit being activated. At 9.30am on Friday six men were arrested in Calais with more than £22,000 worth of newly-withdrawn euros in their pockets. Much more had been taken in earlier raids, including at least £135,000 worth of euros from machines in Dunkirk, and £27,000 in Béthune. All of those arrested were carrying scores of Barclays bank cards, many of which are believed to have been handed over willingly by members of London's large Slovakian community. Robbery: The thieves emptied cashpoints across northern France during the two-hour spree It is not yet known exactly how the gang acquired all of the cards or what effect the withdrawals would have on the account holders and their legal positions. However, it was last night believe that most were handed over by other Slovakian nationals living in the UK, along with their pin numbers, in exchange for the promise of large amounts of cash in return. Like all bank cards, they were able to be used in numerous machines, and not just ones run by Barclays. 'Whoever was responsible for this scam worked out how to use the Barclays card abroad without any credit limit, and had got lots of Slovakians based in Britain interested,' said the source. Investigators working for Frances specialist technical fraud unit, the OCLCTIC admitted they were initially baffled as to how the Slovakians had pulled the scam off. Although some of the cards may have been stolen, they believe the majority had been handed over with PIN numbers by Slovakians nationals in Britain who were on a promise of receiving lots of free money. The main point is that there was no cash limit on withdrawals, said an OCLCTIC source. Bank customers using cards in their own country can expect a withdrawal limit of around 200 a day, but that was not the case here. Unlimited money could be withdrawn from an account, even if there was technically hardly anything in it. Slovakian gangsters have traditionally been at the forefront of ATM scam technology, said the source. They have worked out all kinds of tricks, usually using sophisticated devices which they often attach to cash points. Of the 34 arrested on Friday, all have since been released, with four on bail and facing charges of swindling within an organised gang. They were travelling in Porsche Cayenne 4x4s which had arrived from Dover by ferry. It is thought that many of those released were unwitting accomplices, who had simply been told to use their Barclays cards as much as possible after arriving in France. Detectives said that Barclays had blamed the security breach on a 'computer bug' which has now been eliminated. A Lille police spokesman said: 'Four of the 34 arrested on suspicion of being members of a gang intent on fraud will appear in court at a later date. All of the money retrieved has been confiscated by the judicial authorities.' Fraudulent cash withdrawals are a growing problem in the UK with their cost estimated at more than £60million a year, but this is believed to be the first time that a gang has learned how to use British cards to withdraw unlimited amounts of money abroad. Slovakia has a notorious mafia, with members frequently implicated in organised crime scams across the world. The country joined the EU in 2004, with Slovakians now making up the second largest group of East European immigrants to Britain after Poles. A spokesman for Barclays said: 'Last week we identified and resolved a short-term issue regarding debit card withdrawals at a few ATM sites located outside the UK. The UK ATM network was unaffected by the issue. 'We've been proactively contacting customers who may have been impacted. We are conducting a thorough investigation into this matter and, if fraud has occurred, Barclays will engage in its usual money-recovery activities.'