Policemen are treading into minefields because we have a discipline system that will automatically look at complaints like this

Federation representative David Nixon

But officers told him using the term was banned because it had connotations with slavery.

Afterwards officers said the English language had become a "minefield" of political correctness for the police.

When told about the phrase, Mr Denham told delegates: ""It does show there are phrases in our language that we are not aware of."

But home secretary David Blunkett called the ban "absurd".

Federation representative David Nixon, called for a more "tolerant, realistic attitude towards language".

'Over cautious'

The police constable, who works in Camden, north London, said he had dealt with several cases where officers have been accused of breaching the police code of conduct for using apparently innocuous words.

"Nobody knows what the standard is and so you just don't know the rules," he said.

Mr Denham: Unaware phrase was offensive

"It's a hugely problematic area. You can find officers in trouble through no awareness that they were doing something wrong. It makes them over-cautious and inhibited.

"Policemen are treading into minefields because we have a discipline system that will automatically look at complaints like this."

He cited the example of one officer, with 30 years service, who had even been criticised by a disciplinary board for using the term WPc rather than Pc.

He said the term "pikeys" used to describe a particular type of criminal usually from the travelling community was frowned upon.

Mr Blunkett dismissed the "nitty-gritty" ban as "absolute silliness" that distracted from the real issue of tackling racism in the police.

But he applauded "what the police have been doing very effectively in many areas in cutting out and improving awareness".

Slave ship

"There has been a major problem," Mr Blunkett told the BBC's Today programme.

"It is being overcome. There is a long way still to go."

"Nitty-gritty" is banned because it is thought to originate from a slave traders' phrase to describe the debris left at the bottom of a slave ship after a voyage.