Detectives investigating an alleged plot to blow up planes are conducting a major search for evidence at woods near the scene of one of the raids.
Earlier police raids took place close to the woods
Police and security service officials brought in powerful lights during the night at King's Wood near High Wycombe in Buckinghamshire.
Officers are continuing to question 23 people arrested in the inquiry.
Earlier, Home Secretary John Reid said "at least four major plots" have been thwarted since the 7 July 2005 attacks.
Properties and woodland searched by police in High Wycombe
According to BBC home affairs correspondent Daniel Sandford officers were looking for possible signs of makeshift explosives and detonators in King's Wood.
The home secretary, meanwhile, has said he thought it was right to keep Britain at the highest possible level of terrorist alert.
But Mr Reid acknowledged the "terribly inconvenient regime" of restrictions imposed on carrying hand luggage was affecting airlines and the travelling public.
He told the BBC News 24 Sunday programme those limits were being reviewed but any new regime would still need to ensure safety.
NEW THREAT LEVELS
Low - an attack is unlikely
Moderate - an attack is possible but not likely
Substantial - strong possibility of an attack
Severe - an attack is highly likely
Critical - an attack is expected imminently
Even if the threat level was reduced to "severe", Mr Reid said it was "highly likely there would be another terrorist attempt and that is one thing of which we can be sure."
Asked whether the four major plots he revealed could have caused a major loss of life, Mr Reid said: "In my view yes, on the information I have received."
Mohammed Sarwar, one of three British Muslim MPs who signed an open letter to Tony Blair warning that UK foreign policy was fuelling extremism, said action had to be taken to stop young Muslims being targeted by fundamentalists.
He told BBC Radio 4's The Westminster Hour: "These fanatics who brainwash these young people and mislead them, we've been demanding that all those people who are distributing hatred literature in universities, in colleges, in front of the mosques, should be dealt with the full authority of law.
"They have no right to be in our country."
Shadow foreign secretary William Hague told the same programme the vast majority of Muslims in the UK were moderates who needed support from the wider community.
"Much of the answer to this lies within our own domestic policy," he said.
"We all have to stand four-square with them in confronting this problem and creating a greater sense of cohesion in our own society and a greater shared identity in Britain."