Hardline Brexiteers have had their chance and failed, Scotland's First Minister Nicola Sturgeon has said.
Ahead of the publication of a detailed study on the implications of leaving the European Union, she said no clarity or certainty has been provided about a so-called hard Brexit's supposed benefits.
This, she said, "presented a golden opportunity" for moderate voices to keep Scotland and the UK in the European single market.
She also warned time was running out to prevent the "economic disaster" of a hard Brexit.
Scottish Government analysis, published on Monday, sets out the impact on Scotland's future economic growth of three options for the future UK relationship with Europe - if the country cannot remain members of the EU.
The study - Scotland's Place in Europe: People, Jobs and Investment - looks at continued membership of the single market, a preferential trade agreement or non-preferential access on World Trade Organisation provisions.
Nine months remain for the UK Government to negotiate a deal with the EU and Ms Sturgeon said Theresa May must put the interests of jobs and living standards ahead of internal Tory party obsessions.
She said: "More than 18 months on from the Brexit vote, it beggars belief that the UK Government is not only still unable to say what kind of relationship it wants with the EU, but has also failed to produce any meaningful economic assessment of the different possibilities. Bluntly, the hard Brexiteers have had their chance and failed."
She added: "They have completely failed to explain how their approach could even remotely come close to replacing the enormous lost trade and investment of leaving the single market.
"That means there is now a golden opportunity for those moderate voices who are making the case for Scotland and the UK to remain in the single market. It will be a fundamental dereliction of duty as Prime Minister if Theresa May continues to pursue her red lines without providing information on their impact and publicly discussing the options available.
"Of course, there is no alternative arrangement that can deliver the jobs, people and economic benefit that come from remaining members of the European Union - but if the UK continues down the path of leaving the EU, it is the Prime Minister's duty to do as little harm as possible to the economy.
"The Scottish Government is absolutely clear that, if the UK is indeed leaving the EU, then it must stay within the single market and customs union to prevent needless job losses and cuts in living standards."
A UK Government spokeswoman said: "We are seeking a deal that works for the whole of the UK, that delivers on the result of the EU referendum.
"Rather than trying to undermine the result of a democratic referendum, we urge the Scottish Government to work with us to ensure, as we leave the EU, we protect the UK's vital internal market. Scotland trades four times as much with the rest of the UK as it does with the EU, so it is vital that we ensure that market continues unimpeded."