Britain’s financial watchdog has said it is “highly unlikely” it will meet a deadline set by MPs of next Friday to publish a full report into high street lender RBS’s mistreatment of business customers.

The Treasury select committee, led by Nicky Morgan, gave the Financial Conduct Authority (FCA) the ultimatum on Wednesday, and said it would consider using Parliamentary powers to compel publication if it did not meet it.

Ms Morgan said: “I am pleased to see that the FCA is trying to get the report agreed for publication or handed to the Committee to meet its deadline.”

The FCA argues it cannot put the report in the public domain without the consent of all parties identified directly or indirectly in it – a process known as “Maxwellisation” that typically takes months to complete.

“If the Committee decides itself to publish the report, it will no doubt want to consider carefully the precedent of publishing a document obtained from the FCA under Parliamentary Privilege where the FCA considers that it is legally constrained from publishing the document itself,” FCA chief executive Andrew Bailey said.

An already published summary of the report found “widespread inappropriate treatment” of firms transferred to GRG, with one in six put in additional financial distress as a result of the unit’s actions.