By William Maclean, Security Correspondent

LONDON, April 11 (Reuters) – A police sweep probing a possible al Qaeda plot in Britain raises the question of whether the Pakistani government has the ability to help its former colonial ruler act against Islamist militants.

Many analysts say it is unrealistic of Britain to expect maximum cooperation as long as the Pakistani state is unable or unwilling to crush the guerrillas now striking its own heartland in Punjab, as well as in tribal areas on the Afghan border.

“There is denial in Pakistan about the nature of the threat,” said Hassan Abbas, a Harvard University research fellow and former border-area Pakistani police chief.

“Secondly, anti-Westerner views and in particular anti-U.S. views in Pakistan are kind of obscuring Pakistan’s vision at this moment in facing militants in the tribal areas.”

British blundering has been a feature of the latest raids which saw 12 men — most of them Pakistanis — held on Wednesday in northwest England in one of the largest sweeps on groups suspected of plotting attacks in Britain.

In Islamabad, a foreign ministry official said Pakistan was still awaiting evidence confirming their Pakistani nationality.

The raids had to be brought forward after a senior police officer was photographed openly carrying a secret document revealing plans for the raids. He later resigned.

In a further humiliation for British authorities, which have long maintained they are tackling abuse of the immigration system, newspapers said some of the Pakistanis had been working as security guards after entering Britain on student visas.

But analysts said the bigger question was about Pakistan’s ability to help Britain act against suspects.

“Rather than fretting about visas, we need to get to the roots of the problem: Islamic fundamentalism and terrorism in Pakistan,” wrote The Independent daily.

“The U.K. is getting the blowback from the failure of the Islamabad government to dismantle the terror groups which continue to operate from within Pakistan’s borders.”

For Britain the stakes could not be higher.

Since Sept. 11, 2001, most plots to attack civilians in Britain have had links to Pakistan, including suicide bombings which killed 52 people on London’s transport network in 2005.

Jonathan Evans, the head of the MI5 security agency, told British newspapers in January three out of four al-Qaeda and Islamist-related plots in Britain had a link with Pakistan.

To date, the authorities have concentrated on second and third generation Britons of Pakistani origin – “home grown” militants who travel to Pakistan or Afghanistan for training at guerrilla camps and then return to Britain to carry out attacks.

A SHIFT IN STRATEGY?

While no charges have been brought in the latest case, investigators are urgently looking at the possibility that it represents a different method of al Qaeda operation in which Pakistanis are sent directly into Britain on student visas.

A British counter-terrorism source said of this possibility: “We are keeping an open mind. It’s still early days. A very large amount of material has to be looked at.”

Peter Bergen, a writer on al Qaeda, said: “U.K. officials may not say it openly, but they feel privately that they have made a dent in the ‘home grown’ trend. And they may be right: There have been many prosecutions and arrests in recent years.”

“In that case, the possibility arises that al Qaeda has sought to shift strategy to avoid detection.”

Anthony Glees, director of Britain’s Brunel Centre for Intelligence and Security Studies, said a possible shift in tactics by al Qaeda was “highly worrying”.

“Security and intelligence officials still have a very incomplete picture of what has been unfolding, but if these people were members of a terrorist network then it could well represent a changed direction for al Qaeda,” he said.

Sajjan Gohel of the British-based Asia-Pacific Foundation research institution said British authorities had devoted a large amount of resources in recent years to researching home-grown militants as a result of the 2005 attacks.

“But this scenario is different,” he said. “It means you want to be able to stop them in Pakistan before they ever get here, and that is problematic due to the situation in Pakistan.”

U.S. commanders have made public accusations that Pakistani intelligence has kept ties with militants cultivated in the 1980s, when Pakistan backed anti-Soviet Afghan guerrillas.

Pakistan denies duplicity.

Hassan Abbas said Pakistan, facing a huge security crisis of its own, lacked the capacity to tell London rapidly of possible military training in Pakistan of suspects held in Britain.

“I doubt anyone is going to be able to get this information and give it to you quickly enough for your investigation,” he said. But there was also a political element: Anti-Americanism in Pakistan posed problems for counter-terrorism efforts by the new civilian government.

“The problem the government faces is that when they take a strong view on militants, the opposition benefits politically, especially if the Western world is seen as providing insufficient financial aid to Pakistan. For the government, it’s a lose-lose game.” (Editing by Jonathan Wright)