Heathrow could shrink to a single runway airport with proceeds from redevelopment of the site used to part fund a £50 billion Thames Estuary hub.

The claim came from London mayor Boris Johnson’s aviation advisor Daniel Moylan.

He said he did not believe the case for a new hub for the capital rested on closing Heathrow and outlined a scenario that saw Heathrow becoming “a smaller point-to-point airport serving the west London and home counties premium leisure market”.

Relocation of major airlines, including British Airways, to the new hub would see Heathrow passenger volumes fall from 70 million to 20 million a year.

Arguing that “there will never be a third runway at Heathrow”, he said he believed that in the “right financial circumstances”, BA would welcome having a new airport built around its needs, the Daily Telegraph reported.

“If Heathrow were a smaller airport that could potentially operate with one runway and with fewer terminal facilities, then part of the site becomes available for development,” Moylan said.

“You could also bring in services that are now at Northolt and free that up for development. It’s a large site adjacent to the A40 – there must be value in that.”

He accepted such a plan would involve billions of pounds of compensation for Heathrow owner BAA, as well as airlines forcibly relocated, with industry experts believing the bill could easily reach £15 billion.

Moylan admitted “we are talking about a sum of money to compensate appropriate transition costs” on top of the £50 billion for the new airport.