Terrorists had planned to blow up 10 US-bound planes by mixing a British sports drink with a gel-like substance and were hoping to stage a practice run followed by actual attacks "within days", security officials said on Friday.

Cracking down on the funding of the suspects, the Bank of England [Images] on Friday froze the accounts of 19 of the 24 arrested men. Many of them are believed to be Britons of Pakistani origin.

"The Bank of England has today directed that any funds held for or on behalf of the 19 individuals must be frozen and that no funds should be made available directly or indirectly to any person, except under the authority of a licence," the bank said in a statement.

The 24 men arrested in overnight raids in Britain had not bought plane tickets, but were in the process of surfing the Internet to find flights that had similar departure times.

The suspects were planning to stage a test run within a couple of days, US intelligence officials said.

The plan involved mixing a sports drink with a gel-like substance to explosives that could be ignited with an MP3 player or cell phone.

The sports drink could be combined with a peroxide-based paste to form a potent explosive cocktail, counterterrorism officials said.

As many as 50 people were involved in the plot and the British police were conducting raids across the country to catch more suspects.

Police said they have detained the key players, but believe the network involved is large and global.

Five more suspects are still at large in Britain and are being urgently sought, US media reported.

Many of those being questioned are believed to be Britons of Pakistani origin although police have not confirmed that.

British and Pakistani authorities teamed up to thwart the attacks.

Pakistan Foreign Office spokesperson Tasneem Aslam said on Thursday that seven persons have been arrested in connection with the terrorist plot to blow up commercial airlines during flights from the UK to the US.

Two of the suspects left martyrdom tapes, sources in London [Images] said.

The plot was uncovered after a British agent infiltrated the group giving the authorities intelligence on the alleged plan.

Two of the suspects had recently travelled to Pakistan and later received money on wire. The suspected terorists had been under surveillance in Britain since December, 2005.

Meanwhile, air travellers continued to face delays after Britain raised its security alert to critical and imposed severe restrictions on what passengers are allowed to carry in planes.

Chaos continued at UK airports with Heathrow the worst affected. Thousands of flights have been cancelled and many more delayed.

There was strict frisking with passengers not even allowed to carry water bottles and mothers asked to taste their babies' milk before it could be taken onto flights.

Heathrow Chief Executive Tony Douglas said there would "invevitably" be delays at the airport on Friday and passengers should come prepared.

The plot was targeting United Airlines, American Airlines and Continental Airlines flights to New York, Washington and Los Angeles.