They were born in Britain and brought up as Christians. But they converted to Islam, and now Brian Young and Don Stewart-White are under arrest over the alleged plot to blow up aircraft flying from Britain to America.

In total, 22 of the 24 people arrested in connection with what officials called a plan "to commit mass murder on an unimaginable scale" are still being questioned. The Met police has been granted warrants to detain them until Wednesday.

One has been released without charge, while another's hearing for further detention was adjourned until Monday. That person will remain in custody over the weekend.

The swoops early on Thursday were triggered by the arrest of Rashid Rauf, a British citizen, in Pakistan, according to security sources quoted by the Times.

Rauf's brother Tayib, 22, was arrested in Birmingham and is on a list of 19 terror suspects whose assets were frozen under an order from the Treasury.

Rashid Rauf is no stranger to the law. He left Britain in 2002 after his uncle, Mohammed Saeed, 54, was stabbed to death that April. West Midlands Police seached the Rauf family home in Ward End, Birmingham, but Rashid Rauf was never arrested or charged.

A Pakistani security official told Reuters Islamabad put Rauf under surveillance a tip-off from Britain that he was in the country. "He has been staying here for quite some time and he has been under strict surveillance since then," the unnamed official said.

It is thought British security officials feared the suspected UK plotters would flee or put their alleged plan into action if they lost contact with an important link in Pakistan.

Most of the British suspects had Pakistani roots, except for Don Stewart-Whyte and Brian Young. Both shunned their Christian roots, grew beards, started wearing traditional Islamic dress and married Muslim girls.

The 20-year-old Whyte, the son of Tory activists from High Wycombe, changed his name to Abdul Waheed.

Young, 28, who was born in High Wycombe years after his parents left Caribbean for better life in Britain, became Umar Islam.

Britain remains on "citical" alert - its highest threat level - with almost no hand luggage being allowed on flights. All liquids are banned.

Police believe the alleged plotters aimed to carry liquid explosives on board in drink bottles and cause it to explode mid-flight with detonators disguised as electronic gadgets.

On Friday night transport secretary Douglas Alexander said the draconian restrictions, which allows only the barest essentials like passports and wallets as carry-on luggage, are unlikely to remain indefinitely.

But there would be no return to the lenient measures of before, he warned after a meeting between ministers and aviation bosses in Whitehall.

Airports have started returning to normal, but passengers were advised to check with their airlines before they travel.