The Royal Bank of Scotland's treatment of small businesses may be "the largest theft ever", an MP has claimed.

Labour's Clive Lewis made the comments amid a flurry of condemnation in the Commons over how the bank's global restructuring group (GRG) operated.

MPs heard that the GRG "was more like an abattoir" where firms were "stripped and taken apart", as well as suggestions this was part of an "intended and co-ordinated strategy".

Leading a backbench business debate, former shadow business secretary, Lewis said: "We do know that 90% of GRG administered businesses never made it back to mainstream banking. This is a very high proportion.

"The cost of this is immeasurable but we believe it to be in the tens of billions.

"So let's be clear here. This is the potential size of the injustice that has taken place in our country.

"If it is this big, it may be the largest theft anywhere, ever.

"And if we begin to take into account the opportunity cost to the economy of business failure and businesses that have been unable to grow, if we begin to include the job losses, homes, the losses of health, relationship and lost taxes, we can see the costs are likely to be immeasurable."

MPs heard that businesses were "carved up like a Sunday roast" and only placed in GRG because they wanted to move banks or had made a complaint.

Lewis said: "Since 2008, we know that 16,000 small businesses were put into GRG and the vast majority of them were liquidated.

"I think that tells you all you need to know. This was meant to be somewhere where they were put back to try to get them into a situation where they would come back as a viable business.

"Actually, it was more than an intensive care unit, it was more like an abattoir, where they were actually stripped and taken apart."

Ahead of the debate the Treasury select committee published a memo called "Just Hit Budget!" sent to GRG staff in 2009 and released by the bank to MPs.

It told staff that "sometimes you need to let customers hang themselves", under the heading "rope".

Conservative MP and committee chairwoman Nicky Morgan said the memo "lifts the lid on a culture at RBS".

She added: "When I hear constituents and others say that they will never trust a bank again, they will never ask a bank again for money, then this should be a chilling moment for all banks involved in lending and working with SMEs."

Liberal Democrat leader Sir Vince Cable, the former business secretary, said: "The BBC have actually a seen a copy of the final report, which contains the following incriminating phrase.

"Management knew or should have known that this was an intended and co-ordinated strategy, and that the mistreatment of business customers was a result of that.

"And that the head of GRG responsible for that policy, Mr Nathan Bostock, is now chief executive of Santander."

Lewis's motion calls for an independent inquiry into how financial institutions treat small and medium-sized businesses, and a new tribunal system to deal with financial disputes involving SMEs.