Prime Minister Theresa May is to urge the first ministers of Scotland and Wales to back her Brexit deal at a summit in London.
The leaders of the devolved administrations will meet UK ministers at Downing Street on Wednesday.
Mrs May said her Brexit plan “delivers for the whole of the UK”, urging others to “pull together” behind it.
However, members in both the Scottish Parliament and Welsh Assembly have overwhelmingly voted against the deal.
MPs are set to hold their “meaningful” vote on the withdrawal agreement hammered out with European negotiators in January 2019.
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Ministers from around the UK will gather for a summit at Downing Street on Wednesday afternoon, with Brexit high on the agenda.
Mrs May will head a team of UK ministers including her de facto deputy David Lidington, the Brexit Secretary Stephen Barclay and the Welsh, Scottish and Northern Irish secretaries.
First Minister Nicola Sturgeon and her Brexit Secretary Mike Russell will be there for the Scottish government, while newly-appointed First Minister Mark Drakeford will attend for the Welsh administration.
Ahead of the summit, Mrs May said she was “confident that what we have agreed delivers for the whole of the UK”.
She said: “This deal honours the result of the referendum – taking back control of our money, laws and borders, protecting jobs and livelihoods, and freeing the UK to strike new trade deals with countries around the world.
“That’s why it is more important than ever that the devolved administrations get behind this deal and listen to businesses and industry bodies across all four nations who have been clear that it provides the certainty they need.”
‘Run down the clock’
Ms Sturgeon said the prime minister should “face up to reality” and extend the current Brexit deadline of 29 March.
She said: “It would be unforgiveable if Theresa May was trying to run down the clock to Brexit day. She must immediately inform the EU that she will seek their approval for an extension of Article 50 if MPs reject her deal in January.
“This will allow time for an alternative way forward to be found, preferably another referendum on EU membership
“With 100 days to go before the UK is due to leave the EU, the UK government must stop threatening the disaster of no-deal, and start putting people’s jobs and living standards first.”
Meanwhile, Chancellor Phillip Hammond has confirmed the Scottish government will be allocated £55m for Brexit preparations in 2019/20, as part of its £2bn spend.
The Welsh Government will receive £31m while the Northern Ireland Executive will be granted £20m.