Business and trade union leaders have joined forces to urge Theresa May to "change course" on Brexit and find a "Plan B".

In a highly unusual move, the heads of the Trades Union Congress (TUC) and the Confederation of British Industry (CBI) sent a joint letter to the prime minister demanding that she rule out a no-deal Brexit and seek an extension long enough to secure a withdrawal agreement.

TUC general secretary Frances O'Grady and CBI director general Carolyn Fairbairn warned that the country was facing a "national emergency" and said leaving without a deal would cause "reckless damage".

They urged the prime minister to adopt a "new approach" in order to find a compromise that parliament could support.

It came as Ms May travelled to Brussels to ask EU leaders to delay Brexit until the end of June.

The decision not to seek a longer extension angered many pro-EU MPs, who insisted that three months was not long enough to ensure that a deal is agreed.

Ms O'Grady and Ms Fairbairn warned the prime minister that she should not try to force MPs into a binary choice between her deal and no deal.

In a letter to Ms May, they said: "Together we represent millions of workers and tens of thousands of businesses. It is on their behalf that we are writing to you to ask you to change your Brexit approach.

"Our country is facing a national emergency. Decisions of recent days have caused the risk of no deal to soar. Firms and communities across the UK are not ready for this outcome. The shock to our economy would be felt by generations to come."

The pair asked her to take steps "to protect the jobs, rights and livelihoods of ordinary working people", including ruling out no deal and seeking an extension "long enough for a deal to be agreed".

They said: "'The current deal or no deal’ must not be the only choice. A Plan B must be found - one that protects workers, the economy and an open Irish border, commands a parliamentary majority, and is negotiable with the EU. A new approach is needed to secure this – whether through indicative votes or another mechanism for compromise.

"We cannot overstate the gravity of this crisis for firms and working people. We request an urgent meeting with you to discuss our concerns and hear your response."

The CBI, which speaks for 190,000 businesses, has previously expressed support for Ms May's deal, while the TUC, which represents more than 5.5 million workers, is pushing for a fresh referendum.