Prime Minister Tony Blair said Tuesday that an Al Qaeda terrorist attack in Britain is inevitable and that no amount of government planning could completely defend the country.

His comments during a lengthy question-and-answer session with lawmakers came as British police continued a broad anti-terror crackdown triggered by the discovery of the deadly poison ricin in London.

In the latest police action, officers staged a dramatic pre-dawn raid Monday on a mosque known as a center of radical Islam, seizing documents and arresting seven men in connection with the Jan. 5 poison find.

"I think it's inevitable that [Al Qaeda] will try in some form or other, and I think we can see evidence from the recent arrests that the terrorist network is here, as it is around the rest of the world," the prime minister said.

Blair's government has issued several general warnings that Britain could be a target in the wake of Sept. 11. Blair told Parliament last month that "barely a day goes by" without some new piece of intelligence warning of threats to British interests.

Blair said Tuesday his government was spending "hundreds of millions of pounds" to prepare for a possible attack. "We could spend tens of billions of pounds doing it, and we could still not identify where the attack was actually going to come from."

Also Tuesday, detectives pored over documents seized in Tuesday's raid on the Finsbury Park mosque, the base of the radical Egyptian-born cleric Abu Hamza al-Masri.

Police wearing bulletproof vests used ladders and battering rams to storm the mosque at 2 a.m. They found no evidence of ricin but seized computers, passports and credit cards and found a stun gun, an illegal canister of CS gas and a blank-firing imitation gun.

In France, RTL radio and LCI television reported Tuesday that French passports were found during the raid. The reports provided no further details, and British police would not comment.

Police were questioning the seven suspects -- six North Africans, ages 23-48, and an Eastern European, 22, arrested under terrorism laws. Officers have 72 hours before they must charge or release the men.

Security officials had the mosque under surveillance for months before the raid, suspecting it of being a fertile recruiting ground for extremists. Previous worshippers there include shoe-bomber Richard Reid and extremists who plotted to blow up the U.S. Embassy in Paris, officials say.

Since the ricin find, news reports have said security agencies are investigating an Algerian extremist network in Britain, possibly linked to Algeria's Armed Islamic Group.

Police have described the four men arrested in connection with the ricin find as North African. Two more North Africans were arrested in connection with a Jan. 14 raid in the northern city of Manchester, during which a policeman was stabbed to death when a suspect broke free and grabbed a knife.

Algerian community leaders say dozens of Algerian extremists have come to Britain in recent years to escape a crackdown by French authorities. Mohammed Sekkoum, head of the Algerian Refugee Council in London, has said that as many as 100 Algerian terrorists have entered Britain in the past two years.

Al-Masri, the mosque's firebrand preacher, is wanted in Yemen on terrorist charges and under police surveillance. He was not arrested in the raid, but the government has ordered him removed from his pulpit because of his anti-Western sermons.

Al-Masri denies any link to terror activities, though the mosque was used for a rally marking the first anniversary of Sept. 11, during which radical Muslims praised the attacks as revenge on the United States for its Mideast policies.