Lord Marshall said suggestions that Mr Ayling's position was now in doubt were "idiotic and ridiculous". He added: "There is absolutely no danger to Bob's position over this."
Mr Ayling was the main architect and driving force behind BA's plan to merge its transatlantic business with American, unveiled over two years ago. But last week BA abandoned a full-blown alliance for up to five years, blaming unacceptable regulatory demands and the downturn in the market.
Lord Marshall said BA would now press ahead with expanding its "Oneworld" alliance with American, Canadian Airlines, Qantas and Cathay Pacific. Iberia, the Spanish flag carrier, has already agreed to join. Other airlines within Europe with which BA has code-share-agreements, such as LOT and Malev, are also likely to come aboard.
Lord Marshall maintained, however, that a full alliance with American was still BA's goal even though it would take a long time to achieve.
Lord Marshall also said BA would not attempt to thwart plans by British Midland to launch transatlantic services from Heathrow. Sir Michael Bishop, the British Midland chairman, is set to announce plans later this week to start up to four routes to the US.
This will require amendments to the current bilateral air services agreement between the UK and US, which permit only two British carriers - BA and Virgin - to operate to the US from Heathrow.