The UK's Airports Commission is expected to recommend Heathrow as the preferred site for London's new runway, the BBC reported quoting sources.

The commission is due to make its recommendation early today (1 July).

While backing Heathrow, the commission is also expected to leave the door open for alternative expansion at Gatwick.

The commission's report is not binding on the government.

The BBC said that with no clear decision, the report is likely to cause a split in the ruling Conservative government over which airport to back for an expansion.

It says a new runway at Heathrow could affect the constituencies of at least five Conservative cabinet ministers: Home Secretary Theresa May, Foreign Secretary Phillip Hammond, Chief Secretary to the Treasury Greg Hands, International Development Secretary Justine Greening and Northern Ireland Secretary Theresa Villiers.

Both London Mayor Boris Johnson and Richmond Park MP Zac Goldsmith who hopes to replace him as mayor, are also opposed to the Heathrow site expansion plan.

Chris Lynch, the head of global aviation at PA Consulting, the management consultancy, told The Times: "Whatever decision is made, judicial review is going to be the next step. Both parties have so much at stake that you're going to be looking at some kind of legal action."

The Campaign to Protect Rural England and the Teddington Residents' Association are also considering legal action over Sir Howard Davies's Airport Commission work.

One aviation industry source said that the Mayor could try to reignite interest in his Boris Island airport, rejected by Davies. Others suggest that Johnson could try to promote the expansion of Stansted Airport. "A 'mega Stansted' could be considered," the source said.