Norfolk's police chief was forced to intervene after his own son displayed abusive banners taunting officers taking part in a riot training event.Chief constable Ian McPherson's 17-year-old son was among members of the public simulating a crowd during public order training at the former RAF Coltishall airbase last week.

Norfolk's police chief was forced to intervene after his own son displayed abusive banners taunting officers taking part in a riot training event.

Chief constable Ian McPherson's 17-year-old son was among members of the public simulating a crowd during public order training at the former RAF Coltishall airbase last week.

But his involvement was cut short after he unfurled a banner reading “I am the son of McPherson” along with abusive slogans branding female police officers lesbians and making derogatory comments about Norfolk's diving unit which was controversially scrapped by Mr McPherson last year.

Although the unpaid volunteers, all students, taking part in the demonstration had been briefed to “tease officers”, these actions were judged to over-step the mark. No other banners had been displayed by fellow participants.

After Mr McPherson intervened, his son apologised to those taking part and accepted that his behaviour had been unacceptable. He told 50 officers gathered for the exercise that they were not his views but simply comments he had misguidedly adopted for the purpose of the exercise.

No charges were brought and the force has taken external legal advice to ensure that this was the correct decision. As the incident took place on a private site with no members of the public present, a warning was deemed sufficient.

In a joint statement from Norfolk police and Norfolk Police Authority, a spokesman said: “An incident involving an inappropriate banner waved during a police training session to manage hostile crowds was properly dealt with and resolved at the time.

“The young volunteer responsible made an immediate and sincere apology, explaining that the views expressed were not his own.

“Norfolk Police Authority has been briefed about a subsequent investigation following allegations made on a confidential police reporting line. They support unequivocally the actions taken by the constabulary.”

One officer, who declined to be named, said: “It has all been very embarrassing for the chief.

“The comments caused a lot of offence. The force has been going through upheaval recently and people are still coming to terms with that. The comment about the dive squad in particular was a direct reference to something many people still feel strongly about and was particularly insensitive.”

Earlier this month Mr McPherson confirmed he was considered leaving Norfolk after being shortlisted for the role of assistant commissioners for territorial policing with the Metropolitan Police.

The CPS and IPCC were both consulted about the incident but having heard of the immediate response by Ian McPherson decided that no further action was necessary.