London (CNN) An influential cross-party group of MPs is moving to wrest the initiative over the Brexit process from UK Prime Minister Theresa May. CNN has learned that they are planning to introduce legislation on Monday that would scupper the government's Withdrawal Bill and block a "no-deal" Brexit.

The word in the Westminster corridors Friday was that this unprecedented cross-party "insurgency" was gaining strength. The government's "Plan B" -- which is due to be set out on Monday and debated in the House of Commons the following week -- would be rendered null and void if the MPs legislation were passed.

Among the MPs behind the measure is the Conservative Nick Boles and Labour's Yvette Cooper and Hilary Benn. However, they and other supporters of the legislation will need to work with the Speaker of the House to get parliamentary time for their proposal.

A critical part of the bill -- dubbed European Withdrawal 3.0 -- would postpone the UK's departure from the European Union on March 29 if parliament fails to agree on a way forward by then. That is the day on which Article 50 -- the timetable for the UK's withdrawal -- expires. Any extension would have to be agreed by the other 27 members of the EU.

According to a research paper just published by the House of Commons library, the bill means that "the government would be compelled to request an extension of the two-year negotiating period under Article 50." It says "the drafters of the Bill specifically contemplate an extension of just over 9 months, from 29 March 2019 to 31 December 2019."

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