British Airways has reserved the right to take legal action against Heathrow operator BAA over the chaotic opening of Terminal 5.

The news follows threats of legal action against BAA by ­rival carriers whose moves into the space vacated by BA have also been held up.

BA chief executive Willie Walsh told a committee of MPs last week that a delay in completing the terminal building led to a reduction in training for BA staff and was the single biggest reason for the chaos.

He declined to blame BAA, but said: “We have reserved our position in relation to compensation.”

Walsh confirmed BA had no relationship with any other Terminal 5 supplier, including the builders of the terminal and suppliers of the baggage system and software. “Our relationship is solely with BAA,” he said.

The BA boss admitted he took a risk by not postponing the opening on March 27, but said to do so would have cost more than the subsequent disruption.

Walsh said: “If we had not gone ahead the cost would have been significantly greater than the cost of the problems now – many times greater.” He added: “It is fair to say BAA would have put pressure on us to move.”

BA estimates the cost of the delayed and cancelled flights and misplaced bags in Terminal 5’s first five days at £16 million and Walsh said: “Our reputation was clearly damaged.”

BAA chief executive Colin Matthews suggested an investigation might make matters worse, saying: “It would put pressure on people to be ­defensive and risks discouraging BA people from collaborating with BAA.

He said he would do all he could to prevent an atmosphere of finger-pointing and blame.

He added BA is by far the biggest airline at Heathrow and successful operation of the terminal, particularly the baggage system, depends on co-operation between BAA and BA staff.