Sporadic incidents have broken out between supporters of local rivals

Carl Puiy, Suffolk Police's Superintendent, said it was feared local rivalry was more likely to trigger trouble than problems between England and Croatia fans.

He has sent letters to 10 Norwich supporters who are either convicted hooligans or known troublemakers and is keeping an eye on others.

He told BBC Look East: "We're co-operating very closely with our colleagues in the Norfolk Constabulary and other clubs around the country."

Phil Ham, of the football fanzine Those Were The Days, said: "The Football Association are very keen to stop any trouble at England games, because of the threat that games will be played behind closed doors or we could be banned from future competitions."

About 40 CCTV cameras are in position at Portman Road stadium and local shops have been told not to sell drinks in glass bottles.

Jonathan Hare, who runs a local wine shop subject to the glass bottle ban, said he is concerned about a climate of rowdiness.

He said: "The next thing you know, you've got eight people in here saying 'cor, why aren't you selling any beer, mister?' and suddenly it's my fault and not theirs because they've chosen the wrong outlet."

Suffolk Police said they will not hesitate to arrest anyone they think is out to cause trouble.