Police say that they have made more than 100 arrests in connection with illegal gaming on Westminster Bridge since November 2012.
According to Westminster Police, the gaming scams are run by "professional, organised criminals from eastern Europe who are highly skilled in conning unsuspecting visitors to London out of their cash in card games".
They always have look-outs to spot police officers and always use stooges to tempt innocent victims into betting and handing over sometimes large amounts of cash.
Police say that gang members also dress in costumes – such as Shrek or Charlie Chaplin – and approach tourists on the bridge to insist that they pose for a picture, before intimidating the victim into handing over a cash reward.
Westminster Police say that they have a combination of uniformed and plain-clothes patrols on the bridge each week to try to clamp down on the gaming scams.
"Since November 2012 we have made over 100 arrests and seized large quantities of illegal gaming paraphernalia, costumes and cash," said Westminster Police in a statement.
"The courts are imposing more severe sentences including a recent custodial imprisonment of five months for a first-time offender."
Earlier this month a 20-strong team from Westminster and Lambeth police, safer transport and council teams rounded up five unlicensed traders selling food from carts on Westminster Bridge.
All five were searched, checked and had their carts and foodstuffs seized.
During the operation 12 costumes were also seized and handed over to Westminster enforcement officers. Three people were arrested for illegal gaming and begging. Two were charged and remanded in custody for court.
"The teams always receive appreciative positive comments from tourists and visitors on Westminster Bridge who have repeatedly made known their support of seeing police and council taking robust action against such blatant and wanton crime at an iconic sight in London," said a Westminster Police spokesman.