LONDON, Oct 3: Britain’s ambassador to Afghanistan is understood to have said that the campaign against the Taliban militants would fail and that the best hope was to instal an acceptable dictator in Kabul.

According to a report published in The Times, Sir Sherard Cowper-Coles, “a Foreign Office heavyweight with a reputation for blunt speaking”, is said to have delivered his bleak assessment of the seven-year Nato campaign in Afghanistan during a briefing with a French diplomat, according to French leaks.

However, sources in Whitehall said the account was a parody of the British ambassador’s remarks.

The Times report said François Fitou, the deputy French ambassador to Kabul, told President Sarkozy’s office and the foreign ministry in a coded cable that Sir Sherard believed that “the current situation is bad; the security situation is getting worse; so is corruption and the government has lost all trust”.

According to Mr Fitou, Sir Sherard told him on September 2 that the Nato-led military operation was making things worse. “The foreign forces are ensuring the survival of a regime which would collapse without them . . . They are slowing down and complicating an eventual exit from the crisis, which will probably be dramatic,” the ambassador was quoted as saying.

Britain had no alternative to supporting the United States in Afghanistan, “but we should tell them that we want to be part of a winning strategy, not a losing one”, he was quoted as saying.

“In the short term we should dissuade the American presidential candidates from getting more bogged down in Afghanistan . . . The American strategy is doomed to fail.”

The foreign and Commonwealth office said that the cable did not accurately reflect the views of the ambassador. It is understood that the meeting between Sir Sherard and the French envoy did take place, but that the French account of it is regarded in Whitehall as a gross distortion.

The French foreign ministry did not deny the existence of the cable but it deplored its publication by Le Canard Enchaîné, the investigative weekly. “I am not alarmed because I know that this is not the official British position,” a spokesman told The Times.

Claude Angeli, the veteran Canard journalist who reported the cable, said that he had a copy of the two-page decoded text, which was partly printed in facsimile in his newspaper. “It is quite explosive,” he told The Times.

“What I did not say is that our French diplomats quite agree with the British.” Mr Angeli also reported that the French had been told that Britain aimed to withdraw its forces from Afghanistan by 2010.

The pessimistic view in the cable is common among French diplomats and military officers who are concerned by President Sarkozy’s strong support for the Nato operation in Afghanistan and his recent reinforcement of the French contingent. There was suspicion in Whitehall that the British position was exaggerated for French purposes.

Sir Sherard, 53, a former ambassador to Saudi Arabia, was sent to Kabul last year to beef up Britain’s role in the campaign to secure the government of President Karzai and combat the resurgent Taliban. In an interview last year, he said that Britain could expect to stay in Afghanistan for decades.

According to the French cable, he said the only realistic outlook for Afghanistan would be the installation of “an acceptable dictator” within five or 10 years and that public opinion should be primed for this.

British insiders said that the ambassador never uttered these words. “The trouble with the British ambassador is that he is always at the high end of gloom and doom when in fact it’s not that bad,” a diplomatic source said.