The UK government is plotting a so-called "Bankers' Brexit", which will ignore the concerns of small and medium sized businesses, according to John McDonnell.
The shadow Chancellor will issue the warning as he addresses the Institution of Mechanical Engineers (IMechE) in London today (27 October).
"They'll cut a deal for finance, but ignore our small businesses and manufacturers," McDonnell will say.
"Labour will fight for all our businesses to have single market access, not just the favoured few. Let me be clear, those who have voted Conservative are not the same as the Tory establishment.
"The simple truth is that the Tory establishment cannot be trusted to make a success of Brexit. They want to take control for themselves, not the many. They want to turn Britain into a Singapore of the North Atlantic."
The left-winger will also warn "hard-won" employments rights will be under threat.
"The Tories would want to strike their own TTIP (Transatlantic Trade and Investment Partnership) deal that would keep in place the backdoor privatisations of our NHS, and they would run down our hard-won employment rights," McDonnell will say.
As for what Jeremy Corbyn and Labour can offer in power, McDonnell will promise to deliver a "People's Brexit".
"Labour will take back the economic levers of power currently in the hands of the EU, such as over state-aid rules, and return them to the people. Not a Bankers' Brexit for the lucky few, but a People's Brexit for the many," he will say.
David Gauke, the chief secretary to the Treasury, hit back by claiming that Labour can only offer "division and incompetence".
Theresa May has ruled out offering a "running commentary" on her Brexit plans, but she has promised to end free movement of people to the UK from the EU.
The pledge has prompted fears of a so called "hard Brexit", which would see Britain breaking from Brussels and trading under default World Trade Organisation (WTO) rules with the bloc.
Ministers are expected to trigger Article 50, the official mechanism to split from the EU, by March 2017. The government is currently facing a legal challenge in England's High Court over whether May has the authority to make such a move without a parliamentary vote.
Corbyn hit the headlines yesterday when he compared the Conservative premier's Brexit plans to Baldrick from sitcom Blackadder.
"I think when you're searching for the real meaning and the importance behind the prime minister's statement, you have to consult the great philosophers," he told MPs. "The only one I could come up with is Baldrick, who says: 'Our cunning plan is to have no plan'."