Britain did not allow CIA planes to use its airports to take terror suspects out of Europe, according to a police report.

An 18-month investigations examined claims that "extraordinary rendition" flights chartered by the US stopped in the UK for refuelling.

It is alleged that the detainees were then flown to other countries where they may have been tortured.

Human rights group Liberty called for the probe but is now refusing to accept the findings.

Director Shami Chakrabarti accused the police of "spin" and questioned whether there had in fact been any investigation.

She said the group had received a letter from the Association of Chief Police Officers only yesterday "refusing" to investigate.

She said: "Over 18 months ago, Liberty wrote to the police expressing concern based upon credible investigations that Britain had been used as a staging post for the CIA's programme of extraordinary rendition.

"We asked for a police investigation. Senator Dick Marty has just issued the Council of Europe official report finding European collusion with extraordinary rendition and blanket "over-flight clearances" for US military flights.

"Coincidentally, Liberty has just received a written response from Chief Constable Mike Todd on behalf of Acpo refusing to commence any police investigation into the allegations.

"An Acpo public statement claimed no evidence had been found. When politicians spin it is disappointing. When police engage in the same activity it is rather more dangerous."

A statement released by Acpo said: "The issue of rendition has been aired extensively in the media and has featured prominently in official reports over a recent period of months.

"Michael Todd, chief constable of Greater Manchester Police, has now examined all of the information available relating to this issue and has concluded that there is indeed no evidence to substantiate Liberty's allegations.

"There was no evidence that UK airports were used to transport people by the CIA for torture in other countries.

"There was nothing to substantiate the claims in the evidence supplied by Liberty."

The "extraordinary rendition" allegations first emerged in September 2005 when a newspaper report claimed that airports at Biggin Hill, Birmingham, Bournemouth, Brize Norton, Farnborough, Gatwick, Heathrow, Luton, RAF Mildenhall, Northolt and Stansted had allowed CIA or CIA-chartered jets to land temporarily.

Liberty wrote to the chief constables of Bedfordshire, Dorset, Essex, Hampshire, the Metropolitan Police, the Ministry of Defence Police, Suffolk, Sussex, Thames Valley and West Midlands on November 30 asking them to seek assurances from the US that it was not using UK airports to transport suspects to countries that torture.

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