Home Secretary John Reid has told US television that police and the security authorities believed their investigation was yielding "substantial material" that will advance their prosecution of the suspects.
"The police and authorities are convinced that there was an alleged plot here. They have intervened, and in the course of the next few days we will wait and see what happens in terms of charges," he said.
But Mr Reid declined to confirm a report by the Sunday Times of London that British police were optimistic they will be able to soon charge more than half the 23 suspects in custody with terrorist offences over the plot.
Most of the 23 can be held until Wednesday before police have to ask a judge to further extend their detention, police say.
Under Britain's anti-terror laws, police can hold them up to 28 days before charging or releasing them.
Chance of attack 'high'
Mr Reid told ABC that authorities still consider the chance of an attack "high" and that it would not be difficult to create the kind of explosive that the alleged plot involved.
Asked how difficult it would be to assemble a bomb on board a plane from volatile liquid ingredients, Mr Reid replied: "It is, in my view, relatively simple to make quite an effective bomb ... and with some effect, though not an entirely disastrous effect on a full airplane."
Men forced off plane
In a separate incident, Muslim leaders in Britain have condemned the decision to remove two men from a flight before it took off from the Spanish port of Malaga for the English city of Manchester after fellow passengers feared they might be terrorists.
Some among the 150 passengers on board the Monarch Airlines flight demanded that air staff remove two men after they expressed alarm about their behaviour early on Wednesday, a spokesman for the airline said yesterday.
Cabin crew informed Spanish authorities of the passengers' fears and the men - who apparently looked Asian and spoke Arabic - were taken off the flight and questioned by police.
The pair flew back to Manchester later in the week and were not arrested by British police.
Khalid Mahmoud, a governing Labour Party MP, told The Guardian the decision was "hugely irrational" and called for the public to "calm down."