The Catholic Archbishop of Birmingham, and the Bishop of Paisley have expressed their sorrow after Friday's foiled bomb attacks in London and Saturday's car attack on Glasgow Airport.

Two men of Asian appearance drove a burning jeep into the main terminal doors of Glasgow Airport on Saturday, one day after two car bombs were foiled in Central London. The police say the attacks in London and Glasgow are linked.

Prime Minister Gordon Brown raised the state of security alert in Britain to "critical" following the Glasgow airport attack, indicating that a terrorist attack is thought "imminent".

The Diocese of Paisley covers Glasgow Airport, Scotland's largest airport. Speaking from Lourdes in France where he is on a diocesan pilgrimage, the Bishop of Paisley, the Rt Rev Philip Tartaglia, expressed his regret over the attack.

"I am deeply saddened at the news of the attack on Glasgow Airport. I commend the swift action of the police and security staff on the scene and welcome the fact that injury to passengers and airport employees was avoided," he said.

"My prayers are with all the staff as they return to work over the next few days and with the passengers who will use the terminal as the building reopens. The Diocese of Paisley will be glad to assist the airport operator in any way possible in the weeks and months ahead."

Glasgow Airport, which sustained some fire damage from the attack, was closed on Saturday and flights were cancelled. It has since re-opened, although cars are no longer allowed to drive directly in front of the main terminal doors.

Other airports, including Birmingham, have now closed the front of their terminals to car drop-offs as part of new heightened security measures.

The Catholic Archbishop of Birmingham, the Most Rev Vincent Nichols, said: "Today security levels in our country are at their highest level. In this situation I remind Catholics of our custom of praying for a safe journey. I encourage Catholics and people of other faiths to ask God's special protection for all who travel."

He added: "I also ask people to be particularly vigilant for the safety of all around them."

The number of police patrolling the streets of London has now been stepped up and officers will conduct random searches on cars approaching major rail stations.

Prime Minister Brown said in a televised statement from Downing Street on Saturday night. "I want all people to be vigilant and support police in light of the difficult decisions they have to make. I know the British people will stand together, united, resolute and strong."