The investigation into an alleged plot to blow up transatlantic airliners has uncovered "substantial material", according to Home Secretary John Reid.
Security was stepped up for most of last week
In an interview with US news channel ABC, Mr Reid said police and security services were "content" with their inquiries into the suspected plot.
He also thanked those in the US who had helped in the investigation.
On Monday detectives were continuing to question 23 people over the alleged plot to blow up the airlines.
It is thought liquid bombs disguised as soft drinks could have been used to bring down planes heading from the UK to the US.
Mr Reid told the US channel's This Week programme it was "relatively simple" to make such bombs.
But he stressed there was a judicial process going on, and it was important to remember it was a "suspected terrorist plot" because nothing had yet been proved.
"I can't comment on specifics but what I can say is that the police and the security authorities are content that their investigation is rewarding substantial material which would allow them to take forward the judicial process," he said.
Detectives working on the Operation Overt inquiry are still searching woodland at High Wycombe in Buckinghamshire and 14 addresses across the country.
Speaking generally, Mr Reid said the type of terrorists the world faced "nowadays" were "unconstrained in both elements of threat" and "in terms of their capability".
He said "chemical and biological, radiological and modern technological means of destruction" were available - "sometimes in relatively simple formats".
"There's a constant battle between ourselves and the terrorists to make sure we can keep ahead of that game."