British Airways has apologised for the disruption to flights

BA halted seven round-trip flights in a third day of disruption at Heathrow.

And the company warned that it could merge some services in the coming days as staff shortages continued.

A spokesman earlier said four domestic flights due to leave on Wednesday had been cancelled on Tuesday, but it otherwise expected a normal timetable.

Our flying programme will be under continuous review over the next few days. We may merge some services to safeguard... reliability and robustness British Airways

Round-trip flights cancelled at Heathrow on Wednesday were two to Glasgow, two to Aberdeen, one to Newcastle upon Tyne, one to Manchester and one to Frankfurt.

BA blamed "ongoing operational difficulties".

A spokesman added: "Our flying programme will be under continuous review over the next few days. We may merge some services to safeguard our operational reliability and robustness.

"If we need to do this the changes will be made well in advance of the departure time to minimise the disruption to our customers."

Problems began on Monday when the airline ditched 50 flights from Heathrow due to technical problems with some transatlantic aircraft and staff shortages.

Apology

The knock-on effect of having planes and crews in the wrong place resulted in a further 31 cancellations at the airport on Tuesday.

Earlier on Wednesday, a BA spokesman had said: "The decision was taken yesterday to make four domestic round-trip cancellations.

"These are the last four in terms of tactical cancellations after Monday's disruption."

On Tuesday, BA's director of operations, Mike Street, apologised to customers for the cancellations and admitted BA had "let them down".

This is a time when BA should be making a mint Simon Calder Travel editor The Independent Stranded choir sing airport blues

Mr Street said: "It was a miserable time for them, we let them down and once again on behalf of BA we're all extremely sorry."

A BA spokesman said staff shortages had been caused by an unexpectedly high staff turnover in the lead-up to the busy summer holiday season.

Simon Calder, travel editor of the Independent newspaper, earlier said that BA's troubles came at a time when the company should be "making a mint".

Instead, it was paying out to put people up in hotels and was losing customers, he added.

At the weekend, the airline struck a pay deal with the union representing check-in staff and baggage handlers, narrowly averting an August Bank Holiday strike.

The airline agreed an 8.5% pay increase over three years as well as �1,000 in three payments to September 2006.

Leaders of the Transport and General Workers Union and the GMB will now back the deal in fresh ballots of the thousands of BA workers affected.