Welcome to Northern Ireland road sign at border between the Republic of Ireland and Northern Ireland in Donegal.

Unless the UK’s withdrawal agreement with Brussels is reopened and the backstop abolished there is no prospect of a deal, No 10 has said.

The strong statement came after the EU pushed back against Boris Johnson’s proposal to implement “alternative arrangements” for the UK-Irish border.

Mr Johnson has said the backstop is “anti-democratic” and must be scrapped.

But Donald Tusk said it was “an insurance to avoid a hard border on the island of Ireland”.

Meanwhile, the government has said UK officials will stop attending most EU meetings from 1 September.

The Department for Exiting the European Union said it would “unshackle” them from discussions “about the future of the Union after the UK has left” and allow them to focus on “our immediate national priorities”.

This week Mr Johnson will meet German Chancellor Angela Merkel and French President Emmanuel Macron for the first time since entering No 10.

Ahead of that, in a letter to European Council President Tusk, he called for the backstop to be removed from the withdrawal agreement reached between the EU and his predecessor, Theresa May, arguing it risked undermining the Northern Irish peace process.

Three times

The border is a matter of great political, security and diplomatic sensitivity, and both the UK and EU agree that whatever happens after Brexit there should be no new physical checks or infrastructure at the frontier.

The backstop is a position of last resort to guarantee that, but if implemented, it would see Northern Ireland stay aligned to some rules of the EU single market.

It would also involve a temporary single customs territory, effectively keeping the whole of the UK in the EU customs union.

Mrs May’s withdrawal agreement has been voted down three times by MPs.

Confused by Brexit jargon? Reality Check unpacks the basics.

A series of voices from the European side rejected Mr Johnson’s assertions.

Mr Tusk said those opposing the backstop without “realistic alternatives” supported re-establishing a hard border.

This was the reality “even if they do not admit it”, he added.

The European Commission said Mr Johnson’s letter did not contain a “legally operational solution” to prevent a hard Irish border.

“It does not set out what any alternative arrangements could be,” a spokeswoman said, and “recognises that there is no guarantee such arrangements would be in place by the end of the transitional period”.

Guy Verhofstadt, Brexit spokesman for the European Parliament, said the backstop was “a vital insurance policy… supported by the people of the island of Ireland”.

And speaking in Iceland, Chancellor Merkel said: “Once we have a practical solution to ensure that the Good Friday Agreement continues to apply, then we don’t need the backstop of course.”

A Downing Street spokesperson insisted the UK government was “ready to negotiate, in good faith, an alternative to the backstop, with provisions to ensure that the Irish border issues are dealt with where they should always have been: in the negotiations on the future agreement between the UK and the EU”.

Presentational grey line

The question is whether Boris Johnson’s letter to the EU is intended as the start of negotiations – or designed to be the end of them.

He’s suggested the only way to get a deal is to take the backstop out. Not to time limit it, or modify it, but to bin it.

But if he has a fully-fledged, different plan up his sleeve, why he isn’t spelling out more detail of those “alternative arrangements”?

And why can’t Downing Street say what additional reassurances would be available to the Irish government in the absence of a backstop, if trade talks falter?

The lack of detail on Plan B has made some critics in his own party wonder if his Plan A is simply to make an offer the EU can’t accept and then blame them for no deal.

But No 10 insists he’d do a deal quickly if the EU was more flexible. In other words, Brussels would be expected to blink first as the prospect of no deal approaches.

So far, though, the EU is staring him out.

Presentational grey line

Labour leader Jeremy Corbyn said it was unclear what the prime minister thought he was negotiating.

“He needs to recognise that by just holding the threat of a no-deal Brexit on 31 October towards the European Union isn’t going to bring about a change, it’s going to make things much worse,” he said.

“He created this arbitrary date by his behaviour during the Tory Party leadership campaign. He needs to wise up and stop the nonsense of 31 October and start talking seriously.”

Withdrawal agreement

Theresa May agreed a deal with the EU on the terms of the UK’s departure. It included how much money the UK must pay to the EU as a settlement, details of the transition period, and citizens’ rights. It also covered the so-called “backstop”, which ensures that no hard border exists between Northern Ireland and the Republic of Ireland after Brexit even if there’s no deal on the future relationship in place by the end of the transition period. So-called ‘meaningful votes’ have been held on Theresa May’s deal three times. On all three occasions, MPs rejected the deal.

Political declaration

Document which sets out proposals for how the UK’s long term future relationship with the EU will work after Brexit, agreed as part of Theresa May’s deal with the EU. The political declaration is not legally binding but would be worked up into a full agreement during the transition period.

No deal

A no-deal Brexit would mean the UK leaving the European Union and cutting ties immediately, with no agreement in place. If MPs do not approve a deal, the UK will leave with no deal on 31 October. The UK would follow World Trade Organization rules to trade with the EU and other countries, while trying to negotiate free-trade deals.

Backstop plan

Currently, there are no border posts, physical barriers or checks on people or goods crossing the border between Northern Ireland and the Republic of Ireland. The backstop is a measure in the withdrawal agreement, between Theresa May and the EU, which is designed to ensure that continues after the UK leaves the EU. It comes into effect only if the deal deciding the future relationship between the UK and EU is not agreed by the end of the transition period (31 December 2020). Until the deal on the future relationship is done, the backstop would keep the UK effectively inside the EU’s customs union but with Northern Ireland also conforming to some rules of the single market. Critics say a different status for Northern Ireland could threaten the existence of the United Kingdom and fear that the backstop could become permanent.

Customs union

A trade agreement under which two or more countries do not put tariffs (taxes) on goods coming in from other countries in the union. The countries also decide to set the same tariff on goods entering from outside the union. The EU customs union includes EU member states and some small non-EU members and forbids members from negotiating trade agreements separately from the EU. Instead trade agreements are negotiated collectively.

Irish border

The border between Northern Ireland and the Republic of Ireland. After Brexit, it will become the only land border between the UK and the European Union.