PM said UK should not get distracted by non-members of government after Rees-Mogg urged country to be ‘difficult’

Theresa May advised the EU’s leaders to ignore the threats of Conservative MPs such as Jacob Rees-Mogg during her appeal for a further Brexit delay at the Brussels summit, senior EU officials have revealed.

The prime minister reassured the EU27 that Britain could be relied upon as a member state and turned fire on her backbenchers, referring to a tweet from Rees-Mogg in which he said the UK should be as “difficult as possible” from inside.

“She made the point that the UK was a serious country and we should not get distracted by some non-members of the government that seemed to be trying to create the opposite impression,” a senior official said.

What does a Brexit delay mean for politics, business, citizens and the EU? Read more

During an hour-long address, May also indicated she was open to a long extension, warning leaders that some Conservative MPs would see a looming cliff-edge as an opportunity to crash Britain out of the EU.

In comments that highlighted how far the prime minister has travelled from her position that a “no deal is a better than a bad deal”, May told the 27 heads of state and government that “cliff edges by some are not seen as pressure but as an opportunity”. “That point was made during the discussion,” senior EU source said.

After seven hours of talks at the special Brexit summit on Wednesday evening, the EU and the prime minster agreed that the UK would be offered an extension until 31 October, with the option to leave earlier if the withdrawal agreement is approved by the Commons.

The Guardian can reveal:

Each additional week as a member state will now eat into the transition period in which the UK wants to negotiate the future economic relationship, and avoid having to trigger the Irish backstop to avoid a hard border on the island of Ireland. The 31 December 2020 end date of the transition period, extendable by up to two years, will not be “revised”, an official said.

Nineteen leaders backed a long extension to 31 December or 31 March, seven were flexible either way – and France stood alone demanding a short extension, potentially ending 22 May before being talked round.

The prime minister has agreed she will not attend a 9 May leaders’ summit in the Romanian city of Sibiu on the future of Europe.

May told leaders that the last time there was real cross-party cooperation in the UK was during the second world war, and that while customs arrangements were being discussed with Jeremy Corbyn most of the talks with Labour were about internally locking in any future government into pursuing a softer Brexit.

The EU’s lawyers warned France that its proposal to throw the UK out if it failed to live up to a promise of “sincere cooperation” as a member state would be illegal.

Belgium held up the seven-hour discussion by asking for tougher language on the UK’s responsibilities as a member state during the extra time in the EU but was bought off with two extra words to the summit communique.

May haggled in the early hours of the morning over the June review point included in the summit communique to reflect that it was not a health check on the UK’s record as a member state but a stock check on progress in the Brexit process. “There was a requirement from the UK to be a little more precise so to avoid any confusion,” an EU official said. “That’s why we ended up with the word progress [in paragraph nine of the text].”

The terms of the new Halloween cliff-edge in 29 weeksdo not rule out a further extension , although a senior EU official said the threshold for a further Brexit delay would be higher.

“Everybody understands that, as they say in the UK, a week is a long time in politics – and we gave 29 weeks”, the official added.

“There have to be very good reasons to extend for another time,” source said. “Therefore there is this expectation that something should happen before. And again, in the [leaders’] discussions some are more keen to bring this process to an end than others.”

Because of the 31 October date, the day before Jean-Claude Juncker’s tenure as European commission president ends, the UK will have to nominate a commissioner for the EU’s executive branch despite the concerns of some in the EU27. “It is one of the inconveniences of this particular date”, an official said.

On Thursday, Arlene Foster, leader of the Democratic Unionist party, and the former cabinet minister Iain Duncan Smith, met the EU’s chief negotiator, Michel Barnier, to lobby for alternative arrangements to the Irish backstop that would keep the UK in a shared customs territory, and Northern Ireland in effect in the single market.

Duncan Smith told reporters: ‘The reason for these discussions is that quite recently a number of EU politicians, not least Mr Varadkar [the taoiseach] and Mr Barnier have all said that in the event of No Deal there would be no hard border between Northern Ireland and the Republic of Ireland which is a significant change so we’re here to discuss both sides of that coin.”