London: British police on Monday hunted for more members of a suspected militant cell in connection with the three attempted car bombings in London and Glasgow.

On Saturday a Jeep Cherokee rammed into the entrance of Glasgow's airport, causing a huge fireball - police arrested the passenger and badly-burned driver.

The attack came 36 hours after police in London found two Mercedes car bombs packed with fuel canisters, propane tanks and nails parked near a crowded nightclub in the bustling theatre district.

Five people were arrested over the weekend but police have yet to specify how many people they are searching for. Police declined to identify any of the people under arrest, but British newspapers said none of those arrested are a British and two are doctors - one an Iranian doctor who worked at North Staffordshire Hospital in central England.

Vehicles have been banned from directly approaching airports and police warned of severe disruption for travellers during the following days at main airports and railway stations, as controls and random searches have increased amidst the ongoing fear of further attacks.

Authorities have set Britain's threat level at "critical", which means the possibility of an attack is "imminent". Home Secretary (interior minister) Jacqui Smith urged the public to be on alert saying that Britain was facing a “serious and sustained threat of terrorism''.

"We are not going to let this terrorism intimidate us," she told British channel Sky News. "But ... obviously we need the increased security measures that are in place and we need the public to carry on being as vigilant as possible."