The prime minister has warned MPs that failing to back her Brexit plan would be a “catastrophic and unforgivable breach of trust in our democracy”.

Theresa May faces almost certain defeat when MPs vote on the deal on Tuesday.

The vote will come just weeks after she delayed the same vote when it became clear MPs would not back the deal.

Writing in the Sunday Express she said MPs should not let down those who voted for the UK to leave the European Union.

“Doing so would be a catastrophic and unforgivable breach of trust in our democracy.

“So my message to parliament this weekend is simple: it is time to forget the games and do what is right for our country,” she wrote.

She described the vote as the “biggest and most important decision that any MP of our generation will be asked to make”.

But she also warned that the UK risked crashing out of the EU with no deal or not leaving the EU at all if MPs refused to back her.

Meanwhile, Downing Street said it is “extremely concerned” over reports that a plot has been launched to wrest control of the legislative agenda away from Mrs May if her deal fails.

The Sunday Times says that the plan by backbenchers would see the government lose control of parliamentary business.

This could threaten the ability to govern and also put Brexit legislation at risk.

The news comes as former Conservative prime minister Sir John Major called for Mrs May to halt Brexit, as it would be “morally reprehensible” to leave without a deal.

And more than 100 MEPs from 26 EU countries have written a letter calling on Mrs May to “reconsider” the UK’s departure from the bloc.

Mrs May also came under pressure from her former Brexit secretary Dominic Raab who told MPs to vote against her deal to show Brussels that the UK would “not be bullied”.

He said the UK “must be willing to leave the EU at the end of March on World Trade Organisation terms”.

On the opposition benches, pressure is also mounting on Labour Party leader Jeremy Corbyn.

There are calls for him to trigger a confidence vote in the government but his shadow chancellor John McDonnell has said this would only be done when “the time is right”.

More from Brexit

On Saturday night it was revealed that 14 military planners have been sent in to key government departments in an attempt to prevent border “chaos” if there is a “no-deal” Brexit.

There are fears of major backlogs involving lorries and goods at ports such as Dover if there is no longer frictionless trade with EU nations, The Observer said.