Heathrow has announced plans to ban night flights to try to boost its ongoing push for a third runway.
The west London hub also revealed it would accept any Government decision to rule out building a fourth runway in the future.
There is currently no ban on night flights, although there is a limit of 5,800 take-offs and landings between 11.30pm and 6am each year.
Heathrow says it will comply with all 11 conditions set out by the Airports Commission, including a key requirement on air quality which stated that new flights would only be permitted if air quality did not breach EU limits.
In a letter to the Prime Minister, claiming expansion would provide a boost to the economy, Chief Executive John Holland-Kaye said: "We have acted now to let you and your government make the right choice. It will enable you to choose Heathrow." He went on to state that expansion would help Britain "win thousands more jobs."
John Stewart, chairman of the main anti-Heathrow expansion group HACAN, said: "Heathrow's decision to move on night flights could turn out to be significant.
"HACAN has long campaigned for a ban on flights before 6am, but things have remained the same for decades. Heathrow's proposals may prise open a door on night flights that has been firmly closed for 25 years."
Gatwick Airport has responded by reasserting its position that it remains the only expansion plan that can deliver for the UK.
CEO Stewart Wingate said: "This is a desperate last throw from a project that has repeatedly failed.
"Heathrow can promise many things but they cannot wish away the reality of its location.
"An expanded Heathrow will impact hundreds of thousands of people currently not affected by aircraft noise – an expanded Gatwick would impact less than 3% of this number."
The manifesto of Sadiq Khan, London's new mayor, stated that he would oppose a third runway at Heathrow.
He pledged to continue to call for expansion at Gatwick as a "more viable, cheaper and easier to build alternative" even if the Government pursues the Heathrow option.
Heathrow airport welcomed over six million passengers in April 2016.
April's passenger numbers were down 1.6% on 2015 due to an earlier Easter holiday, but passenger growth at Heathrow remains strong with volumes up 1.5% so far in 2016.