THERESA May has been accused of a “shameful abdication of responsibility” after failing to define what Brexit means 100 days after the vote to leave the EU.

The SNP marked the milestone by publishing 100 questions for the Prime Minister to answer, adding to the pressure on her to explain the details of Brexit when she makes her first speech as party leader to the UK Conservative conference in Birmingham today.

May is due to speak in an afternoon session called “Global Britain: Making a success of Brexit”, which also includes three prominent Leave campaigners – Brexit Secretary David Davis, Foreign Secretary Boris Johnson and International Development Secretary Priti Patel.

The SNP dossier includes fundamental questions such as when May will trigger the Article 50 withdrawal process and if the UK will stay part of the single market.

There are also specific questions about Scotland and trade, the economy, workers’ rights, free movement, EU funding, justice, health and education.

May, who has so far hidden behind her "Brexit means Brexit" mantra, told the BBC last week she wanted the right deal for Britain “not necessarily the quickest deal”.

SNP Westminster leader Angus Robertson, who has repeatedly asked May at Prime Minister’s Questions about her plans on the single market, said: “We are now 100 days on from the EU referendum result, and the utter lack of clarity from the Prime Minister and the rest of the UK Government is a shameful abdication of responsibility.

“The Tories are in the process of walking the UK economy off a cliff with a vague promise that they’ll find a parachute on the way down. It’s not good enough.

“The SNP’s 100 Brexit questions is by no means an exhaustive list, but is shows the sheer scale of uncertainty facing Scotland and the rest of the UK. This casual approach is putting jobs, investment and economic prosperity at risk.”

Brexit is expected to dominate this week's gathering, despite May’s hope to recast the Tories as the party of ordinary people after the exit of David Cameron and George Osborne.

As the EU Commission’s chief Brexit negotiator, Michel Barnier, started work yesterday, it was reported that EU leaders expect May to trigger Article 50 in the spring so that Brexit takes place before the 2019 European elections.

Diplomats also feel a “hard Brexit” is likely, with the UK leaving the single market and customs union that allows the free circulation of goods in order to limit the free movement of labour.

However a clean-break, also hinted at by International Trade Secretary Liam Fox last week, could end the ‘passporting’ rules that allow UK banks to operate across the EU, with repercussions for London and the Scottish financial sector.

Hard-line Brexiteer Iain Duncan Smith yesterday said May must not go round the EU “on bended knee”, and claimed the UK and Brussels “wanted roughly the same thing”.

After he and other Tory right-wingers published a “Brexit Blueprint” urging an early withdrawal, the former Work and Pensions Secretary told Radio 4 that David Cameron had failed to strike a credible pre-referendum deal in Europe because he went “begging” to his counterparts.

Meanwhile, Tony Blair’s former spin doctor has admitted New Labour contributed to Brexit.

Promoting the Volume Five of his Downing Street diaries, Alastair Campbell said the party failed to respond to growing working-class concerns about immigration.

“The fact that we won two election in 2001 and 2005 despite the Tories campaigning on immigration may also have made us complacent,” he said.

“Just as in Scotland people started to feel Labour support was taken for granted, so in areas of high immigration I think some Labour voters started to feel the same.”

Scottish Labour yesterday accused the Tories of putting the country’s economic prospects at risk through Brexit.

MSP Jackie Baillie said: “Campaigning during the EU referendum, Ruth Davidson viciously attacked leading Brexiteers like Boris Johnson and Andrea Leadsom – now she is preparing to share a platform with them.

“The Scottish Tories have taken a vow of silence over the impact that Brexit will have on our economy. They used to claim they had a long term economic plan, now they can’t even tell us what leaving the EU means.

“How can Scotland believe a word Ruth Davidson says about Brexit?”

Former SNP leader Gordon Wilson yesterday wrote to the Irish and Northern Ireland governments to forge a "Celtic Corridor" with Scotland to boost trade after Brexit.