The UK and European Union are on the threshold of striking a post-Brexit trade deal.

An announcement is expected on Christmas Eve, but talks were continuing through the night on the details of an agreement.

The development came as Britain and the EU were believed to have made progress on resolving issues including fishing rights and the “level playing field” measures aimed at preventing unfair competition.

The expected deal comes with just days left before the current trading arrangements expire on December 31.

Prime Minister Boris Johnson led a late-night call with Cabinet ministers to update them on the situation.

Mr Johnson has been in close contact with European Commission president Ursula von der Leyen in recent days as top-level efforts intensified to get a deal over the line.

The pair are expected to have a further call on Christmas Eve to agree the deal.

European Commission spokesman Eric Mamer suggested an announcement could come early on Christmas Eve.

“Work will continue throughout the night,” he said shortly after midnight.

“Grabbing some sleep is recommended to all Brexit-watchers at this point. It will hopefully be an early start tomorrow morning…”

The UK side expected talks over the legal text of the deal – reportedly around 2,000 pages long – to continue into the early hours.

A deal covering the UK-EU trading relationship worth almost £670 billion will come as a relief to business leaders.

If, as expected, it provides for trade free from tariffs and quotas the economic shock of breaking away from the EU’s single market and customs union will be softened.

The Office for Budget Responsibility had forecast that a no-deal Brexit could wipe 2% off gross domestic product – a measure of the size of the economy – in 2021, adding to the damage to jobs and livelihoods already caused by coronavirus.

But the details of the deal will be closely scrutinised to see where either side has compromised.

It was widely reported Britain offered a longer transition period regarding fishing rights than it previously wanted and would agree to the EU handing back only 25% of its quotas in British waters at the start of the process.

And as the battle to spin the situation began, French sources reportedly claimed the UK had made “huge concessions”, especially on fisheries – a symbolically important issue on both sides of the Channel.

The late-night wrangling on the final aspects of the deal is thought to have included discussions on species of fish as part of the quota arrangements.

Any deal Mr Johnson secures is likely to pass through Parliament with Labour expected not to oppose it – Sir Keir Starmer has stressed that an agreement with the EU would be in the national interest.

But in a sign of the political difficulties Mr Johnson may face, the European Research Group (ERG) of hardline pro-Brexit Tory MPs said they would scrutinise any deal in great detail.

The ERG said it would reconvene its so-called “star chamber” of legal experts to examine the text.

A statement issued by the group on Wednesday said: “Given that the new agreement is also highly complex, the star chamber will scrutinise it in detail, to ensure that its provisions genuinely protect the sovereignty of the United Kingdom after we exit the transition period at the end of this year.”

But it is not only hardcore Eurosceptics who could be critical of a deal.

Lord Barwell, Theresa May’s former chief of staff, said “the truth is the deal means the introduction of significant barriers to free trade” through customs and regulatory checks.

But he acknowledged “it is better than no deal and we could certainly do with some good news”.

The negotiations in Brussels were fuelled by a late-night delivery of pizzas.

If a deal is agreed it would have to be backed by the EU’s 27 member states.

MPs and peers would be recalled to vote on a deal next week, but the European Parliament has said they will not have time to ratify a deal before January 1 – meaning any agreement is likely to be provisional.