A NO Deal Brexit would cause the worst economic crisis for 45 years, the Government's budget watchdog warned today.

Although it said that it still thinks Britain will secure a deal with Brussels by next March, if we didn't then it would have dire consequences for the country's finances - not seen since the three-day week of the Seventies.

Brits could face higher prices, no planes flying, and a slump in the pound, the Office for Budget Responsibility predicted today in a grim assessment.

If No Deal is reached then Britain will be treated "like a third country" and will have "tariffs at borders" come in place - including fresh customs checks.

And although the OBR said there was no direct parallel, it said that when the three-day week was introduced in 1974, they said that it caused economic output to fall 3 per cent.

That would have a "severe short term impact on the economy" by means of "weaker activity and higher prices", the independent watchdog forecasted.

It could lead to:

Significance delays at the border if an agreement were not reached to allow British aircraft to fly within the EU
Businesses and the public could "stockpile goods in advance"
The pound could take a hit because of a lack of confidence about Britain's future
But they did assume that the divorce bill will be paid and that an agreement with the EU will be reached on future trade - and there will be a transition period for businesses and employees to get ready.

It marks the first time the typically reserved OBR has published more than a cursory remark on the potential impact of Brexit.

Previously it has said that it can only do so once it sees the outcome of EU negotiations.

OBR chief Robert Chote enraged Brexiteers two years ago by saying Britain may have to borrow £122 billion because of the uncertainty created by the EU withdrawal.

The latest warnings are set to be dismissed as the latest batch of Project Fear by Brexiteers.

However, several OBR forecasts about what would happen to Britain if we voted to leave have not come through, causing critics to doubt whether they are accurate.

Treasury predictions that thousands of jobs would be lost and the economy would tank if we opted for Brexit have yet to materialise.

Theresa May has said that No Deal would "not be the end of the world" - echoing the words of the World Trade Organisation's chief.

She said she wants to secure an agreement with the bloc but that Britain would thrive no matter what happens.

And Brexit boss Dominic Raab has been helping businesses prepare for a No Deal situation by issuing them a stream of notices.

He has vowed to help Brits prepare for every eventuality possible - and insisted that Britain will be fine outside the bloc.