The letter urges MPs to:“avert an unnecessary self-inflicted national disaster to support a way forward before it is too late.”

It points out that “We are unions not affiliated to any political party and only take strong stances on political issues when they threaten the personal and working lives of our members. Right now, it is imperative our members’ voices are heard.”

The letter also warns about the dangers of no deal but warns that the Prime Minister’s deal has serious flaws, particularly on workers’ rights:

“No trade unionist should be seduced by the warm words of the prime minister on workers’ rights. Accepting the deal would mean dismantling the legal safety net that has underpinned employment rights in this country for decades, and replacing it with a set of empty promises from a government that may not be in office in a year’s time.”

Mike Clancy, Prospect general secretary said: “Despite promising votes on no deal and on extending Article 50, the government is still effectively running down the clock on Brexit, trying to force MPs to back either the Prime Minister’s bad deal or a disastrous no deal.

“No-one voted for the chaos we have seen since the referendum in 2016. It is time for MPs to break the gridlock, take no deal permanently off the table and vote to extend Article 50 so that we can get a solution that brings the country together and protects jobs.

“If the Prime Minister is concerned about wider support she should let the public have the final say on whether to ratify her deal or stick with the benefits we currently get in the EU. This would allow a debate on the known terms of Brexit and offer a way forward that is democratic and deliverable.”

You can read the whole letter here.