Rules on hand luggage liquids have been brought back at London City Airport and five other airports in the UK which had installed new scanners.

The Department for Transport would not disclose a reason for the “temporary” measure and did not confirm how long it would be in place.

However, a spokeswoman stressed there is no specific threat.

At most UK airports, passengers are not allowed to carry liquids larger than 100ml, but at London City, Newcastle, Leeds Bradford, Aberdeen, Southend and Teesside airports this restriction had been lifted following the installation of new security scanners.

A statement from the DfT said: “This temporary move is to enable further improvements to be made to the new checkpoint systems and will only affect a small number of passengers. For most passengers, security measures will remain unchanged.

“Passengers should continue to check security requirements with their departure airport before travelling.”

London City Airport told passengers that although the 100ml limit has returned, it was still possible to keep all liquids and electronic items in bags when going through security.

Birmingham Airport, which became the first major UK airport to complete the installation of the new scanners, is not on the list because it had already kept the 100ml hand-luggage restrictions in place.