Several thousand items of luggage displaced during problems at Heathrow airport over Christmas have still not been returned to their owners, British Airways said today.

The airline - the worst affected by difficulties with the baggage system - said many pieces of luggage remained stacked up at Heathrow terminals one and four while it used air freighter planes to try and clear the backlog.

Around half of the affected items of luggage belonged to BA customers, the airline said.

It denied claims the backlog had happened because too few staff were working on the baggage system, saying it hoped to reunite all passengers with their luggage within 48 hours.

"The problem began before Christmas when there was a fault with a baggage belt at Heathrow terminal four,” an airline spokesman said. “That caused the initial backlog, and about 8,000 bags were not delivered.”

The spokesman said the situation had been compounded by days of heavy fog that caused BA to cancel hundreds of flights before Christmas.

On December 29, there was a further baggage belt problem at terminal four.

"The fog and the second belt problem led to about 10,000 bags not being delivered,” the spokesman said. “We have put on air freighter planes to get the bags to their owners, and we have drafted in a number of volunteers to help.

"To put the whole thing into context, we dealt with about 75,000 bags a day at Heathrow over the festive period and handled about 1m passengers."

It is the second time in six months that thousands of items of luggage have been misplaced at the London airport.

In August last year, at least 10,000 items of luggage were misplaced at UK airports after a security crackdown following disclosures that an alleged plot to blow up transatlantic airliners had been stopped. Heathrow was the worst affected airport.

Today, BA said the latest problems had coincided with changes in working practice for its baggage handlers at terminals one and four.

The changes came ahead of the move of the airline's entire Heathrow operation to the new terminal five in March next year.

BA currently has around 2,000 baggage handlers working between the two terminals, and needs to train all the handlers to operate together in one system.