Before a momentous week in the House of Commons, Political Editor RICHARD PORRITT analyses the potential fallout of the Brexit votes

Eastern Daily Press: The House of Commons will vote on the amendments to the Brexit Bill propsoed by the LordsPhoto: PAThe House of Commons will vote on the amendments to the Brexit Bill propsoed by the LordsPhoto: PA (Image: PA Wire/PA Images)

This is a crunch week.

After a drubbing from the House of Lords, prime minister Theresa May faces a Brexit showdown that will determine what type of exit the UK makes from the European Union.

The votes on the amendments by peers to the EU (Withdrawal) Bill could be very tight. Because Mrs May's government does not have the majority she was so desperate for when she called the snap election last year her leadership is on a knife edge. A bad week for the prime minister could spark a leadership challenge.

Only a dozen or so Tories will need to vote alongside Labour, the Liberal Democrats and the SNP to defeat the government and wreak havoc on Mrs May's Brexit strategy.

The role of parliament in agreeing any final deal with the EU and the customs union are the two votes set to be the closest – and Number 10 is nervous.

Since becoming prime minister in the aftermath of the referendum Mrs May has maintained that for Brexit to mean Brexit the UK has to quit the customs union and the single market. But the Irish border issue has thrown that goal into chaos.

Powerful backbench Brexiteers the European Research Group – led by leadership hopeful Jacob Rees-Mogg – have repeatedly stated that the UK needs a clean, swift and complete break from Europe.

If Mrs May wobbles this week the ERG have the numbers required within Tory party rules to force a leadership contest. And there are plenty of candidates waiting to pounce.

But Mrs May's time in Downing Street has been plagued by disaster after disaster – not least the catastrophic general election campaign – and she has always clung on. The reason is that enough of her MPs will back her – not because they fully support her but because they fear who might follow her through that famous black door.

The majority of Tory MPs wanted Britain to remain in the EU. But the favourites to replace her – Rees-Mogg, Boris Johnson and Michael Gove – are all Leavers. This has spooked a lot of Tories and kept Mrs May in place.

No Conservatives from our region are expected to rebel and North West Norfolk MP Sir Henry Bellingham believes even those who have voted against the government in the past will now side with Mrs May.

'I believe the government will get the votes through. There is a big difference between what are technical amendments – I would put those down as an attempt to improve the Bill – and some of the amendments which are wrecking amendments because they would delay our departure from the EU or they would fundamentally undermine our negotiating position,' he said.

'For example if parliament can reject the final deal and send the prime minister back that is an open invitation to Europe saying 'don't give anything away until the prime minister is forced back after losing a vote in parliament'.

'I have spoken to a number of Lords who voted for these amendments and I believe these are not amendments they will insist on pushing back time and again – they respect the elected legitimacy of the lower house.

'On the seven or eight fundamental points that will be voted on I think those who have been strong Remainers and have voted against the government in the past will desist from doing so because this is getting very serious and the clock is ticking.'

But it is not just the Conservatives who face a tricky week. Labour is also a party that is has deep divisions on Brexit.

There was anger from pro-EU Labour MPs last week when party whips demanded they did not support the Lords amendment on staying in the European Economic Area. Scores of MPs are set to defy this order – including several senior figures.

But Ipswich MP Sandy Martin is confident if his party focuses on pushing for a Brexit deal that safeguards jobs they can become a united force.

'In my view there is a real danger to jobs and the economy of this country if we leave the EU without a really effective deal,' he said. 'Anything which is a viable alternative to leaving without a deal should be pursued.

'Labour is focussed on a Brexit deal that protects jobs – that has always been our position. In that context I want us to do the best we can to ensure the government cannot take us out without a good deal. I don't believe we can do that unless we all stick together.'

It is set to be a defining week for Brexit – and the fallout could start political tremors that will be felt for a long time to come.