BBC Radio 5 Live

Callers are discussing the Northern Ireland border on BBC Radio 5 live.

Simon, a supporter of Brexit from Leicester, says "the peace process is far more important than Brexit".

"We had 3,000 people die and tens of thousands were injured.

"We cannot let peace slip through our fingers."

Some have argued that staying in the customs union would allow the UK to leave the EU while avoiding a hard border on the island of Ireland.

Simon asks: "How much would staying in the customs union affect the UK?"

BBC Reality Check's Chris Morris says: "Your view of the customs union is dependent on your politics.

"Some say it is helpful to business because it removes import taxes.

"Those who don't like it say being in a customs union would limit the UK's ability to make trade deals."

Today Programme
BBC Radio 4

Former clerk of the House of Commons Lord Lisvane says it is "very surprising that the prime minister says she is not prepared to do what the House of Commons asks her do to".

"I accept there may be things which are not negotiable, but to say in advance I'm not committing to do what Parliament wants is quite a step," he says.

He says the current situation is "a failure of politics not of Parliament", and urges against making rushed changes to parliamentary procedure.

"The car goes into the ditch you look at the driver - you don't immediately start looking at the engine."

Steve Brine says in his resignation letter to the PM: "You cannot wish away no deal, you can only do that by having a deal."

He says that it looks like a "tall order" for the PM's deal to pass the House of Commons so "we are left in a position where the House must find a common position that can".

He adds that his belief is that the only way to achieve that is by a series of "indicative" votes.

BBC Radio 4

Former deputy prime minister Lord Heseltine tells BBC Radio 4's Today programme the prime minister is “playing with fire when she says she’s not going to take any notice of what the House of Commons says".

Although MPs decided on Monday night they would hold votes on various Brexit options on Wednesday, Theresa May said there was no guarantee she would abide by the result - because "the votes could lead to an outcome that is un-negotiable with the EU".

Lord Heseltine - a retired Conservative MP who now sits in the House of Lords - added that Mrs May's premiership had been "hanging by the flimsiest thread now for some weeks".

Today Programme
BBC Radio 4

Former clerk of the House of Commons Lord Lisvane says "a general election now would be a Brexit election".

He says issues such as crime, health and education "would take a back seat".

"That would be a great shame," he says.

Today Programme
BBC Radio 4

Former director of legislative affairs at Downing Street, Nikki da Costa, says there are two ways a general election could happen.

Firstly, two thirds of MPs would have to vote for a general election. She suggests that because Labour and the SNP would be likely to support this, a fresh election would be approved.

Alternatively, she explains, the government could lose a vote of no confidence.

"There would then be fourteen days in which the government could try to regain the confidence of the House.

"If that doesn't work and no one else can command a majority, then you would head towards a general election."

BBC Radio 5 Live

Conservative MP Richard Harrington, who resigned last night, tells the Today programme Brexit must be delivered but "not at the price of suicide".

Health Secretary Matt Hancock told the Today programme a little earlier that it was clear - even for colleagues who wanted a no-deal Brexit - that the House of Commons was not going to let it happen.

Our BBC poltiical correspondent tweets:

The Labour Party's general secretary Jennie Formby, who on Monday said she had been diagnosed with breast cancer, says she is "back to business as usual".

Although Ms Formby is starting treatment this week, she said she will continue to work as much as possible.

Today Programme
BBC Radio 4

Matt Hancock says he worries that in the process of delivering Brexit "there are many, many parts of our constitution that are being stressed."

"We don't have a God-given right to be successful," the health minister says.

"But one of the reason we have been so successful in the past is because our constitution has worked well and been flexible.

"I worry about what happens when we start breaking those conventions."