At least 10,000 bags checked in by British Airways passengers have gone missing at airports since the UK security alert began, the airline says.
Many passengers are still waiting to get their luggage back
It said half of them were still piled up at airports waiting to be delivered back to their owners.
A war of words has erupted between BA and airport operator BAA over who is to blame for the misplaced luggage.
BA has cancelled 700 Heathrow flights since Thursday, after requirements to check in hand luggage caused delays.
It is considering seeking compensation from airport operator BAA.
A friend of Tayib Rauf (left) released footage of him at the family business
BA boss Willie Walsh said BAA's management had had "no adequate plan" to deal with the emergency.
The airline said: "We fully apologise that customers have not been able to travel with their baggage on certain flights throughout the past five days of unprecedented circumstances at Heathrow.
"This is due to a combination of issues with the BAA's baggage systems which have all contributed to the situation."
The BBC's transport correspondent Tom Symonds said Heathrow's "fairly antiquated" baggage system had had to check in small items such as handbags and mobile phones that it could not easily handle.
Stephen Nelson, chief executive of BAA, apologised for problems with lost baggage but said it was not the time for "finger pointing", It had been an "unprecedented circumstance", he added.
Other airlines have not released figures for how much baggage they have to return to their passengers and will only say that their problems are not on the same scale as BA's.
All UK airports have now relaxed the restrictions on hand luggage introduced following Thursday's terror alert.
Passengers had initially been banned from taking anything into aircraft cabins except travel documents, baby food and certain medicines, all of which had to be carried in clear plastic bags.
They are now allowed to carry on a small bag, but they are still not allowed to take in any liquids apart from baby milk, baby food and prescription medicines.
Passengers are warned this does not constitute a "return to normal" and they should still expect delays.
TUESDAY FLIGHT CANCELLATIONS
Heathrow - 47 flights, mostly BA, cancelled
Stansted - 8 Ryanair flights cancelled
Gatwick - 11 domestic BA flights initially cancelled but re-instated at 1230 BST
Airports including Birmingham, Newcastle, Manchester, Edinburgh and Glasgow reported as being mostly back to normal.
BA says it is planning to operate 90% of its schedule on Wednesday.
It plans to cancel three long-haul and 32 short-haul departures out of Heathrow from a typical daily schedule of about 280 departing flights.
The official terror threat to the UK was downgraded on Monday from "critical" to "severe", meaning an attack is now considered highly likely but not imminent.
Twenty-four people remain in custody after another person was held under terror laws over the alleged plot on Tuesday.
And CCTV footage has emerged of one of the men being held, Tayib Rauf, at his father's business hours before he was arrested.
It was released by one of his friends, who said it proved Mr Rauf was innocent of allegations.
Meanwhile, police are continuing to search woodland near High Wycombe.
Officers have also searched at two internet cafes 18 miles away in Slough.
Police said they had executed 46 warrants and were still working on 22 properties. They had also searched 20 vehicles, they said.
One man was arrested in the Thames Valley area on Tuesday lunchtime, police said.
Meanwhile, an investigation has been launched after a 12-year-old boy managed to board a plane at Gatwick without tickets during the security alert.
The boy, thought to have run away from a care home in Birkenhead, Merseyside, was heading to Lisbon and discovered on the flight before it took off on Monday morning.
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