West Midlands Police said on Wednesday it had made an official complaint to television regulator Ofcom over a documentary about extremism in British mosques, saying the footage had been misleading.

The Channel 4 Dispatches programme "Undercover Mosque", broadcast in January, purported to show extremist speeches being delivered at mosques in London and Birmingham.

The claims were investigated by West Midlands police officers who found there was no evidence to bring charges against three speakers featured in the documentary.

Instead, prosecutors said the footage, which provoked anger among Britain's 1.7 million Muslims, had been taken out of context.

"The splicing together of extracts from longer speeches appears to have completely distorted what the speakers were saying," said Crown Prosecution Service lawyer Bethan David.

"In this case we have been dealing with a heavily edited television programme, apparently taking out of context aspects of speeches which in their totality could never provide a realistic prospect of any convictions."

After their initial investigation, police turned their attention to whether the programme-makers themselves were guilty of inciting racial hatred.

However, detectives concluded there was not enough evidence available and instead have made a formal complaint to Ofcom.

"The priority has been to investigate the documentary and its making with as much rigour as the extremism the programme sought to portray," Assistant Chief Constable Anil Patani said.

Channel 4 hit back, saying the police had no evidence for their allegations.

"We believe the offensive views expressed by the people revealed in the programme speak for themselves," a spokesman said. "We didn't put these words into people's mouths and all extracts were carefully contextualised."

However Shazad Anwar, chief executive of Muslim youth organisation the Ramadhan Foundation, said the police's decision was a "total vindication" for groups that had complained the programme had been a distortion.

"Channel 4 should hang their head in shame and apologise immediately for the hurt they have caused those people," he said.

The news is the latest controversy to embroil the publicly-owned broadcaster.

In May, it was severely criticised by Ofcom for "serious editorial misjudgement" over it handling of a racism row on last year's "Celebrity Big Brother" show.

Premium phone regulator ICSTIS imposed a record 150,000 pound fine on Channel 4 in July over a show which asked viewers to telephone to take part in a quiz even though winners had already been chosen.