The Scottish Parliament will today vote against Theresa May’s proposed Brexit deal, with MSPs calling instead for a “better alternative” to the PM’s plans be taken forward.

Four of the five political parties at Holyrood – the SNP, Labour, the Greens and Liberal Democrats – will unite to back a joint motion, which also makes clear their opposition to a no-deal Brexit.

Constitutional Relations Secretary Mike Russell said the debate was an “historic opportunity for the Scottish Parliament to come together and formally oppose both a ‘no deal’ option and the Prime Minister’s damaging Brexit deal”.

But the Tories, who will be the only party to vote against the motion, claimed the SNP and Scottish Greens were using the debate to try to push for a second vote on Scottish independence.

It comes just six days ahead of the “meaningful vote” at Westminster, when MPs will have their say on the PM’s Brexit deal.

While Holyrood voting against the proposals will not stop the UK Government from trying to push through its plans, it will put the Scottish Parliament on record as opposing both the agreement and the prospect of a no deal Brexit.

The joint motion argues the draft withdrawal agreement and political declaration will be “damaging for Scotland and the nations and regions of the UK as a whole and therefore recommends that they be rejected and that a better alternative be taken forward”.

Speaking ahead of the debate, Mr Russell said: “The Prime Minister’s Brexit deal will make Scotland poorer and deliver continued uncertainty. It will mean years of further negotiations with no guarantee that a trade deal with the EU will even be agreed.

“This is a historic opportunity for the Scottish Parliament to come together and formally oppose both a ‘no deal’ option and the Prime Minister’s damaging Brexit deal.”

Scottish Government analysis of the PM’s draft deal to leave the European Union indicated this could result in “loss equivalent to £1,610 per person in Scotland compared to EU membership by 2030”.

Meanwhile separate documents published by the UK Government showed it could cut the country’s GDP by up to 3.9% over the next 15 years compared to staying in the EU – while a no-deal Brexit could cause the economy to shrink by 9.3% over the same period.

Mr Russell said: “The UK Government’s own analysis, as well as the detailed assessment from the Scottish Government, shows why the draft Brexit deal is unacceptable – it would make us poorer while extending uncertainty.”

After “cooperation” by different parties to draw up a joint motion, he added Holyrood should “now reach a consensus and oppose both the proposed draft Brexit deal and the suggestion a no-deal Brexit is the only alternative”.

But Scottish Conservative constitution spokesman Adam Tomkins was clear his party would vote “in defiance of the SNP’s games”, saying: “The Scottish Conservatives will, alone, oppose the motion set out by the SNP, Labour, Lib Dems and Greens today.

“We know what the SNP and Greens are trying to do with this needless debate – they want to use it to manufacture yet more grievance as part of their push for a second independence referendum.

“That Labour and the Liberal Democrats have once again fallen into line with the nationalists is disappointing but hardly surprising. It’s a choice they’ve taken at every step since the Brexit referendum was held.

“Willie Rennie and Richard Leonard are Nicola Sturgeon’s little helpers.”

Mr Tomkins added: “The Scottish Conservatives are the only party committed to respecting the results of both referendums we have held in the last four years.

“That clear, democratic principle is one we will seek to uphold in the Scottish Parliament today”