The EU has said Britain cannot delay Brexit without a clear plan for what happens next, indicating only an election, a new referendum or major compromise on Theresa May’s red lines will suffice.

In an ultimatum, Michel Barnier said there would need to be a “new event or new political process” to secure an extension to the Article 50 negotiating period.

Brussels’ intervention represents yet another blow for the prime minister, who planned to ask for a delay at this week’s European Council meeting as part of a drive to finally push through her twice-defeated Brexit deal.

She is already having to grapple with the new obstacle thrown in front of her by Commons speaker John Bercow who has tried to block her from putting the deal in front of MPs for a third time.

Any move to secure a long delay to Brexit is likely to infuriate Leave-backing Tory MPs and could even lead to cabinet resignations.

A meeting of her top ministers on Tuesday ended with Brexiteer ministers making grave warnings about the collapse of their party if it fails to deliver Britain’s departure.

Theresa May is set to write to European Council president Donald Tusk, laying out her proposal to delay Brexit beyond 29 March – something that requires the approval of all 27 remaining member states at the summit on Thursday.

The Independent understands that one approach being considered is to ask for a lengthy extension to the Article 50 period, with the option of an early break if Ms May can get her deal through parliament.

Tariffs in the event of a no-deal Brexit Show all 15 1 /15 Tariffs in the event of a no-deal Brexit Tariffs in the event of a no-deal Brexit Pork There will be tariffs on pork in order to protect British farmers Getty Tariffs in the event of a no-deal Brexit Cheese There will be tariffs in place on some cheeses including €22.10/100kg of cheddar, €19.10/100kg of processed cheese and €18.60/100kg on some blue cheeses Getty Tariffs in the event of a no-deal Brexit Milk There will be no tariffs in place on milk Getty Tariffs in the event of a no-deal Brexit Car Parts There will be no tariffs on car parts imported from Europe PA Tariffs in the event of a no-deal Brexit Cars However finished cars will face tariffs of 10.6% Getty Tariffs in the event of a no-deal Brexit Alcoholic drinks There will be no tariffs on alcoholic drinks - except on some rums due to ingredients used in their distilling process Getty Tariffs in the event of a no-deal Brexit Beef There will be tariffs on beef in order to protect British farmers Getty Tariffs in the event of a no-deal Brexit Fish There will be no tariffs on many types of fish including cod, haddock, salmon and sea bass Getty Tariffs in the event of a no-deal Brexit Fruit and vegetables There will be no tariffs on almost all fruit and vegetables Getty Tariffs in the event of a no-deal Brexit Chocolate There will be no tariffs on chocolate or other cocoa products Getty Tariffs in the event of a no-deal Brexit Poultry There will be tariffs on poultry in order to protect British farmers Getty Tariffs in the event of a no-deal Brexit Ceramics There will be some tariffs in place on ceramis Getty Tariffs in the event of a no-deal Brexit Steel There will be no tariffs on steel Getty Tariffs in the event of a no-deal Brexit Coal There will be no tariffs on coal Getty Tariffs in the event of a no-deal Brexit Lamb/Mutton There will be tariffs on the meat of sheep in order to protect British farmers Getty

But Mr Barnier poured cold water on the idea, telling a reporter who asked him about it: “You said both short and long – well, it’s either one or the other, isn’t it?”

He added: “My feeling is ... a longer extension needs to be linked to something new. There needs to be a new event or a new political process.”

A longer extension needs to be linked to something new. There needs to be a new event or a new political process Chief EU Brexit negotiator Michel Barnier

Mr Barnier told a news conference in Brussels: “It is our duty to ask whether this extension would be useful because an extension will be something which would extend uncertainty, and uncertainty costs.”

He again warned that the UK would need to propose “something new” to justify a lengthy extension.

A “new event” can only really mean giving the British public a Final Say referendum or an election, while a new process is likely to refer to a push to rewrite Ms May’s strategy to include a closer relationship with the EU, possibly a permanent customs union.

The Independent understands that for these things the EU could potentially agree a nine month delay, or a three month delay if Ms May sought a shorter extension to the Article 50 period.

Michel Barnier: 'Everyone should now finalise all preparations for a no-deal scenario'

Mr Barnier’s words were later backed up by Irish deputy PM Simon Coveney who said the UK would have to table a “a new plan of action, potentially a new approach” that has a majority in the Commons.

He added: “I don’t think there’s any appetite amongst leaders to simply kick this can down the road.”

But any move to secure a long extension by Ms May, without the option of a get out, will enflame tensions in her own party.

A hardcore group of Brexiteers have indicated they could even side with Jeremy Corbyn’s Labour in a vote of no confidence in Ms May’s administration is she delays Brexit for too long.

Details of discussions from the morning cabinet meeting were again widely leaked, with angry comments made by Brexiteer ministers.

Andrea Leadsom told colleagues: “This used to be the cabinet that would deliver Brexit and now from what I’m hearing it’s not.”

Michel Barnier questions Brexit delay: 'Why would we extend Article 50 when negotiations are over?'

Liz Truss, who gave an interview at the weekend indicating that she might be tempted to run for the leadership, warned that a failure to deliver Brexit would mean the UK becomes “a barren land ruled by Jeremy Corbyn”.

International trade secretary Liam Fox warned all leadership hopefuls that if their party cannot secure a deal it could be destroyed.

Labour said Mr Corbyn had held “positive and detailed” discussions with members of the “Norway-plus” group of MPs on Tuesday afternoon, who are seeking a relationship in which the UK remains in the single market and customs union.

A spokesperson said: “All participants pledged to work together and with others across parliament to find a Commons majority for a close economic relationship with the EU to break the Brexit impasse and bring the country together.”

Mr Corbyn also held talks with leaders of small parties who are united in calling for a new referendum with a Remain option.

Green co-leader Caroline Lucas said afterwards that progress was “slow”, but added: “He certainly didn’t rule out the idea of a public vote.

“He did say he would have some real concerns about putting Theresa May’s deal to the public vote, a deal that has been lost twice here in parliament, and he would be much happier putting his own version of Brexit to that public vote.