British Airways chief executive Willie Walsh today appealed to business leaders not to judge his company by the disastrous opening of Terminal 5.

In a speech to the Institute of Directors, he admitted the opening of BA's £4.3 billion new home last month was a major disappointment - but stressed that things weremuch improved.

He said: "There is no doubt that 27 March - the opening - was a very difficult and disappointing day for BA and the country. We got things wrong and we let people down. I have apologised to customers, and I apologise again today."

Walsh has faced calls for his resignation over the fiasco but today asked business leaders not to rush to judgment of Terminal 5. Much work had been done since the opening, and there had been a "steady performance increase" in the baggage handling system, he said.

BA's long-haul flights were to have joined the short-haul division at T5 today. ButWalsh said the transfer would now take place on a staged basis, starting next month and lasting until the end of October "at the latest". He said the delays had caused him "acute embarrassment", but said he was still confident T5 would herald a "great era" for BA.

However, he said, it would do nothing to increase runway capacity, and that was why a planned third runway at Heathrow was vital.

"I believe it is in the interest of the country that the reputation of Heathrow is restored on a lasting basis as quickly as possible," he said.

Without the extra capacity, UK businesses could be faced with relocating abroad, and may experience "difficulties in attracting inward investment".

Walsh added that Heathrow was now "full", and flights were subject to more delays than in other European capitals.