A Muslim peer complained that only he and another Asian-looking man had been selected from a queue of about 65 people for a random check at Heathrow.

Lord Ahmed said they were checking in their luggage for a flight to the United States.

On another occasion he had been singled out to have his bags searched, to see if he was carrying any cash, when he was leaving for Saudi Arabia.

The Labour peer asked Government spokesman Lord McIntosh of Haringey whether such random checks were carried out on all passengers, whatever their colour or nationality.

Lord McIntosh told him at Lords question time: "When I was being briefed for this question I said that I had never been stopped when leaving the country, but both the head of frontier security and his colleague told me that they had both been stopped."

Lord McIntosh said Customs and Excise checks were carried out to look for prohibited goods such as illicit drugs; check export licensing requirements; enforce international sanctions and detect crime-related cash.

"All checks are informed by risk assessments which might include the destination country as one indicator.

"I don't want to talk about the risk assessment, because clearly once you start talking about detailed profiles, you start giving people an idea of how to avoid them. But I think it is fair to say that these profiles are strictly adhered to," he said.