Pulling was filmed wearing an improvised Ku Klux Klan mask

The statement, by Northumbria Police chief constable, Chrispian Strachan, follows a BBC documentary, which exposed racism at a police training college in Cheshire.

It also follows an admission from his assistant, Kevin Mathieson, that there are racist officers in the force.

Six officers from the Greater Manchester, Cheshire and North Wales forces have resigned in the wake of the TV documentary.

In it, undercover reporter Mark Daly filmed officers making racist threats and statements about officers from ethnic minorities at the training centre.

Now, the head of the Northumbria force has warned staff that racist behaviour will not be tolerated.

Mr Strachan said: "Inevitably the police service will reflect society in general, but Northumbria Police makes it clear to all staff that racist behaviour in any form, whether inappropriate language, harassment or discrimination, will not be tolerated.

"All Northumbria Police staff undergo diversity training, which is aimed at making people aware of their responsibilities to themselves and others, both within the force and the wider community.

Chrispian Strachan: Racism will not be tolerated

"We work hard to ensure that people within the organisation feel confident to speak out if they encounter any attitudes which they or others find offensive and have support systems, such as a confidential reporting hotline, specifically designed to help anyone in this position.

"Questions on diversity awareness are posed during the police recruitment process and Northumbria probationers receive diversity training in both the centrally provided element of their course and in their local training.

"However, chief constables are asking Centrex, the body which oversees initial recruit training, to take further steps to test the attitude of recruits early in their careers."

Mr Strachan, with other chief constables in England and Wales, has signed a letter to a national newspaper condemning racism in the police service.

In it they affirm: 'There is no room in the British police service for anyone with racist attitudes'.