Airport campaigners might be breathing a sigh of relief after Boris Johnson announced he is not standing for Tory leader.

The former mayor of London was among the front-runners and at one point the bookies' favourite but in a shock move he has announced he will not be standing.

Campaigners had feared, if Johnson was to become the next Prime Minister, plans for an airport in the Thames Estuary would be back on the table.

A decision on airport expansion was due be announced in the next two weeks, but it has been revealed today that it will be delayed until after a new Conservative leader is in place.

A Thames Estuary airport has been ruled out by the Davies Commission which, last July, recommended a new runway at Heathrow.

But the formal decision was delayed by the government in December in order to allow for more environmental study.

Theresa May, who is now the bookies favourite for Tory leader, is MP for Maidenhead. Her stated position is against expansion at Heathrow.

Medway Council had already put aside £15,000 in its budget for a campaign against any possible future airport proposals.

On Sunday, council leader Alan Jarrett said: “We have kept a watching brief on it. As and when we need to be, we will be ready to lobby again.”

The Friends of the North Marshes has already warned there is a chink in their armour if they have to fight an airport again, because of Brexit.

George Crozer, from the friends group, said: “It is a worrying time. Now we have decided to leave the EU, all the laws and regulations that protect the area are up for grabs. The special protection areas and birds directives are all protected by the EU.”

EU nature directives were instrumental in stopping an airport at Cliffe in 2003 and again in 2014, when the Davies Commission ruled out an airport anywhere in the Thames Estuary or on the Hoo Peninsula.

When Sir Howard Davies delivered his final report he said an estuary airport was not plausible because the area is such an important breeding site for birds.

He added: “The European directives say that you can only take away that habitat if it’s the only place you can build an airport and we don’t think we could claim that was the case.”

Last year, when MEPs were discussing nature directives, Gill Moore, from the friends group, said: “Any weakening of these laws could put our most important wildlife sites in the Thames, Medway and Swale estuaries in peril.”