A police community support officer ordered two Christian preachers to stop handing out gospel leaflets in a predominantly Muslim area of Birmingham.
The evangelists say they were threatened with arrest for committing a "hate crime" and were told they risked being beaten up if they returned.
The incident will fuel fears that "no-go areas" for Christians are emerging in British towns and cities, as the Rt Rev Michael Nazir-Ali, the Bishop of Rochester, claimed in The Sunday Telegraph this year.
Arthur Cunningham, 48, and Joseph Abraham, 65, both full-time evangelical ministers, have launched legal action against West Midlands Police, claiming the officer infringed their right to profess their religion.
Mr Abraham said: "I couldn't believe this was happening in Britain. The Bishop of Rochester was criticised by the Church of England recently when he said there were no-go areas in Britain but he was right; there are certainly no-go areas for Christians who want to share the gospel."
Last night, Christian campaigners described the officer's behaviour as "deeply alarming".
The preachers, both ministers in Birmingham, were handing out leaflets on Alum Rock Road in February when they started talking to four Asian youths.
A police community support officer (PCSO) interrupted the conversation and began questioning the ministers about their beliefs.
They said when the officer realised they were American, although both have lived in Britain for many years, he launched a tirade against President Bush and the wars in Iraq and Afghanistan.
Mr Cunningham said: "I told him that this had nothing to do with the gospel we were preaching but he became very aggressive.
"He said we were in a Muslim area and were not allowed to spread our Christian message. He said we were committing a hate crime by telling the youths to leave Islam and said that he was going to take us to the police station."
The preacher refused to give the PCSO his address because he felt the officer's manner was "threatening and intimidating".
The ministers claim he also advised them not to return to the area. As he walked away, the PCSO said: "You have been warned. If you come back here and get beaten up, well you have been warned".
West Midlands Police, who refused to apologise, said the incident had been "fully investigated" and the officer would be given training in understanding hate crime and communication.
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