As the terminal enters its fourth day of operation, British Airways said it expects 85% of incoming and outgoing flights to go ahead, a figure that it hopes will rise to 87% on Monday.

A BA spokeswoman said it hoped things will steadily improve as the week goes on, but admitted: "This is dependent on the performance of the baggage system."

The airline admitted 15,000 bags had gone astray thanks to a glitch with its "complex and sophisticated" luggage handling system.

"It is 15,000 bags we need to reunite with their owners," said a spokeswoman, adding: "To put this into context, we process 75,000 bags every day.

Meanwhile, the Civil Aviation Authority (CAA) has written to British Airways to ensure that the airline has been complying with European legislation on passengers' rights.

"We wrote to them on Friday and will be contacting them as a matter of urgency this week to ensure they are fulfilling the requirements of the legislation, that all passengers should be treated the same," a spokesman said.

The union Unite said Heathrow workers were frustrated that their long-standing concerns about Terminal 5 (T5) had "fallen on deaf ears".

Unite National Secretary for Civil Aviation Steve Turner said workers had raised concerns about feared problems at T5 "over a long period of time".

Those included issues of access through security gates into the terminal and issues relating to the baggage handling areas.