Brexit: Could Britain's withdrawal from EU still be averted?

London: Could Britain`s parliament, a future prime minister or even a second referendum effectively annul the Brexit vote? Constitutional experts say not in the short-term, but the future is uncertain.

Prime Minister David Cameron, who led the campaign for Britain to stay in the EU, ruled such a move out in a parliamentary debate on Monday, telling MPs: "This house shouldn`t block the will of the British people".

That did not stop some MPs from posing the question and the issue is being widely debated among many disappointed "Remain" supporters who are still hoping to avert Britain`s withdrawal from the European Union.

Brexit supporters have said that ignoring the referendum would be unacceptable, but the country is in uncharted territory and nobody knows how long any Brexit negotiations could last.

Britons voted by 52 percent to 48 percent in favour of leaving the EU in Thursday`s shock referendum.

Here are the key questions:

A senior European diplomat on Sunday said their personal view was that London "will never" invoke Article 50 of the EU`s Lisbon Treaty -- the formal mechanism for exiting the European Union.

Cameron has said that formally starting EU withdrawal talks will be a matter for his replacement as prime minister, but none of the victorious Brexit campaign leaders appear in any rush to start what will no doubt be lengthy, complex and painful negotiations.

"Not trigger? It`s possible if the country is in a catastrophic economic situation," said Anand Menon, a European politics professor at King`s College London.

Menon said there was an "80-percent possibility" that Britain would invoke Article 50 and the process could be lengthy as there was a "very high" prospect of a new general election given the current political turmoil.

The lack of a written constitution in Britain makes the picture hazy. leaving some to say that parliament is not obliged to ratify the referendum result.

MPs "don`t have a no," said Alan Renwick, deputy head of the Constitution Unit at University College London.

"It`s a matter for the government," Renwick said.

Some MPs have said the opposite, however.

"The referendum was an advisory, non-binding referendum. We do not have to do this," said David Lammy, a lawmaker from the opposition Labour Party.

"We can stop this madness and bring this nightmare to an end through a vote in parliament. Our sovereign parliament needs to now vote on whether we should exit the EU," he said.

Geoffrey Robertson, a leading lawyer, also said: "It`s not over yet".

"Law which passed last year to set up the referendum said nothing about the result being binding or having any legal force," he said.

"Before Brexit can be triggered, parliament must repeal the 1972 European Communities Act by which it voted to take us into the European Union, and MPs have every right - and indeed a duty if they think it best for Britain, to vote to stay," he said.

Asked about the possibility of a parliamentary blocking vote, Menon said: "Politically impossible. They (MPs) would be slaughtered".

A petition calling for a new referendum had garnered more than 3.8 million signatures by Monday.

But analysts ruled out any new vote right now.

"There is a very powerful principle in British democracy that one vote is enough," said Tony Travers, a professor at the London School of Economics.

"It would be very unwise to hold another referendum, it`s not going to happen," he said.

But a general election could change things.

University of Edinburgh professor Neil Walker said "a fundamental difference of course" could be triggered "if a Brexit government collapsed overnight".

Renwick added: "If the party elected has made the commitment in their manifesto, whether to trigger Article 50 or to call a second referendum, then they would have a mandate for doing that."

Top Brexit campaigner Boris Johnson himself earlier this year was widely interpreted as saying that the referendum might not necessarily mean Britain was out.

He said that only by voting to leave would the country "get the change we need" in the EU.

Johnson later retracted the statement and said: "Out is out".