The former government adviser who claimed in a controversial report that Royal Bank of Scotland forced viable businesses to the wall has launched a fresh broadside at the bank after it was forced to issue an apology to the Treasury Select Committee over misleading evidence given by two executives.

Lawrence Tomlinson said the testimony of Derek Sach, the former head of the RBS global restructuring group, and deputy chief executive Chris Sullivan “makes a mockery of both the parliamentary process and of the SMEs who have suffered as a result of the bank’s action”.

The two men had claimed that the GRG – which dealt with struggling businesses to which RBS had lent money – was not a profit centre, even though, as the bank has subsequently accepted, it was.

Mr Tomlinson’s report, written while he served as entrepreneur-in-residence at Vince Cable’s Department for Business Innovation and Skills, ignited a storm of controversy over GRG and led to a string of investigations.

An RBS-commissioned inquiry by the City law firm Clifford Chance, however, found no evidence to substantiate the claims. Another report, by the former Bank of England deputy Governor Sir Andrew Large, was highly critical of the bank’s treatment of SMEs.

Mr Tomlinson said of RBS: “It’s extremely disappointing that once again RBS has not taken an open and honest approach to dealing with very serious allegations. Once again, we are left to question whether this is incompetence on behalf of the bank or intentional distortion of the facts.”

There was yet more controversy generated by the BBC’s Panorama, which reported that Mr Tomlinson and his business had been forced out of the bank, although it denied that this was as a result of the claims in Mr Tomlinson’s report.

Correspondence between RBS and the Treasury committee over the hearing involving Mr Sach and Mr Sullivan was published at the weekend. It included an apology from the bank.

A spokesperson said: “Both Derek Sach and Chris Sullivan have clarified the evidence they provided to the Treasury committee. The bank has apologised unreservedly for any confusion caused. This was not intentional.”