LONDON, Aug 13 (Xinhua) -- Britain has thwarted "at least four major plots" since the July 7 attacks in London last year, Home Secretary John Reid said on Sunday.

    In an interview with the BBC's News 24, Reid said the plots would have led to significant loss of life had the terrorists not been stopped.

    About two dozen terror investigations were currently being pursued by police, the minister said.

    Reid said that although 24 people had been arrested over an alleged plot to blow up aircraft en route to the United States on Thursday, there was still "a substantial threat" to security in Britain.

    "We think we have the main suspects in this particular plot," he said, adding, "I have to be honest and say on the basis of what we know, there could be others out there ... so the threat of a terrorist attack in the UK is still very substantial."

    Reid said that the current security measures at UK airports would be "time limited".

    A new set of airport security procedures including compulsory body searches and the banning of hand luggage, led to further delays and cancellations of flights at Britain's airports.

    Britain raised its security alert to "critical", the highest of five levels, from "severe" on Thursday, where it had been for about a year since being relaxed in the weeks after the London transport attacks that killed 56 people. Enditem