LONDON/BRUSSELS • A deal to smooth Britain's departure from the European Union hung in the balance yesterday after diplomats indicated the bloc wanted more concessions from Prime Minister Boris Johnson, and said a full agreement was unlikely this week.

As the Brexit maelstrom spins ever faster, Mr Johnson and EU leaders face a tumultuous week of reckoning that could decide whether the divorce is orderly, acrimonious or delayed yet again.

Mr Johnson says he wants to strike an exit deal at an EU summit on Thursday and Friday to allow an orderly departure on Oct 31, but if an agreement is not possible he will lead the United Kingdom out of the club it joined in 1973 without a deal - even though Parliament has passed a law saying he cannot do so.

EU politicians such as Irish Foreign Minister Simon Coveney said a deal was possible but that much more work was needed.

However, EU diplomats are pessimistic about the chances of Mr Johnson's hybrid Customs proposal for the Irish border riddle.

"We are not very optimistic," a senior EU diplomat told Reuters.

After more than three years of Brexit crisis and tortuous negotiations that have claimed the scalps of two British prime ministers, Mr Johnson will have to ratify any last-minute deal in Parliament, which will sit in an extraordinary session on Saturday for the first time since the 1982 Falklands War.

If Mr Johnson is unable to clinch a deal, an acrimonious divorce could follow that would divide the West, roil financial markets and test the cohesion of the United Kingdom.

The main sticking point remains the border between EU member Ireland and the British province of Northern Ireland: how to prevent it becoming a back door into the EU after Brexit without erecting controls that could undermine the 1998 peace agreement that largely ended three decades of sectarian violence on the island.

The details of Mr Johnson's proposals have not been published but are essentially a compromise in which Northern Ireland is formally in the UK's Customs union - and informally in the EU's Customs union.

"Such a hybrid Customs territory like the British are proposing for Northern Ireland does not work anywhere in the world, it seems," an EU diplomat said.

In a sign that the Brexit optimism which followed Mr Johnson's meeting with Irish Prime Minister Leo Varadkar last week may have been premature, EU diplomats now say the best chance of a deal would be to keep Northern Ireland in the EU's Customs union.

That would be a step too far for Mr Johnson's Northern Irish allies, the Democratic Unionist Party, and Brexit supporters in his Conservative Party.

If he fails to strike a deal with the EU, a law passed by his opponents obliges him to seek a delay - the scenario that EU diplomats think is most likely.

"It's up to the Brits to decide if they will ask for an extension," European Commission head Jean-Claude Juncker said in an interview with Austrian media outlet Kurier.

Extension options range from as short as an extra month to half a year or longer, and the other EU states would need to agree unanimously to grant it.

REUTERS