Outgoing president of the European Commission Jean-Claude Juncker has told Boris Johnson that the EU will not be renegotiating the withdrawal treaty, meaning the prime minister will have to make good on delivering a no-deal Brexit on October 31st.

Delivering his first statement to the House of Commons as prime minister on Thursday, Mr Johnson again pledged that the UK will be taken out of the EU on October 31st with or without an exit agreement with Brussels, and that failure to do otherwise “would cause a catastrophic loss of confidence in our political system”.

The prime minister stayed wedded to his preference to leaving the EU with a deal, however, despite numerous warnings from European leaders and EU bureaucrats that the treaty, with his contentious Irish backstop, would not be renegotiated.

“I believe that is still possible even at this late stage and I will work flat out to make it happen,” Mr Johnson said on Thursday,  adding: “I, my team, and my Rt Hon Friend the Secretary of State for Exiting the European Union are ready to meet and to talk on this basis to the Commission or other EU colleagues whenever they are ready to do so.”

Rather than the EU being “equally ready” to reopen talks “in the spirit of friendship” as the prime minister hopes, President Juncker told Mr Johnson in a telephone conversation that evening that the withdrawal treaty is the “only agreement possible”, reports The Guardian.

The proposal was also rejected by the EU’s chief Brexit negotiator Michel Barnier on behalf of the European Council, which is comprised of the heads of government of EU member states, writing in an email to EU diplomats that the EU27 would not deviate from their position and called Mr Johnson’s language “combative”.

Mr Barnier wrote: “PM Johnson has stated that if an agreement is to be reached it goes by way of eliminating the backstop. This is of course unacceptable and not within the mandate of the European council.”

Adding that the bloc would be “ready” for a situation where the prime minister prioritises planning for a clean break, he said: “No-deal will never be the EU’s choice, but we all have to be ready for all scenarios.”

While the day before, leading figure in the liberal-progressive movement in the European Parliament Guy Verhofstadt reacted to the comments Mr Johnson made outside of Number 10 on a no-deal Brexit, saying that the withdrawal treaty was “not up for renegotiation”.

Mr Johnson has maintained throughout his months on the backbench after quitting Theresa May’s government that he would not support the withdrawal agreement; however, on the third vote he backed the deal. That incident, amongst others where the Conservative politician flip-flopped on his position, has given rise to concerns that he may not keep to his word over the Halloween deadline. His predecessor, after all, had publicly pledged 108 times to take the UK out of the EU with or without a deal on March 29th, 2019.