A Clifford Chance (CC) investigation into lending practices at the Royal Bank of Scotland (RBS) has been by criticised by the author of the report that instigated the probe.

CC's independent report, which was published last week, found "no evidence that RBS systematically set out to defraud its business customers".

The review was carried out in response to allegations in a report by Dr Lawrence Tomlinson that the bank's global restructuring group (GRG) put various business customers "on a journey towards administration, receivership and liquidation".

Tomlinson said it was "unsurprising" that CC did not find any clear evidence of fraud, something which Tomlinson said he had never accused the bank of.

"It's important to note that Clifford Chance did not investigate or reach conclusions on areas such as the validity of valuations and treatment of businesses," said Tomlinson, a former entrepreneur-in-residence at the Department of Business Innovation and Skills.

"I look forward to the [Financial Conduct Authority] publishing their findings later this year as their scope is much more robust, far reaching and, of course, independent."

For the report, CC interviewed 138 small business customers in the recovery unit, 45 employees and reviewed 130 files, comprising 400,000 pages and 1,200 documents.

CC identified several cases where RBS customers felt unclear of the way the bank charged fees, and allegations around the behaviour of RBS staff, although "no evidence" of this was found.

The bank also agreed to waive default interest for 90 days and wind down West Register – the vehicle the bank uses for bidding on property – acknowledging the perceived conflict of interest.

"We could not let this allegation hang over us," said the bank's CEO Ross McEwan. "That's why we acted quickly to appoint Clifford Chance to get to the truth of this claim. We are determined to earn back the trust of our customers."

Tomlinson said the CC report, which was overseen by regulatory partner Carlos Conceicao (pictured), made for damaging reading.

"I am struggling to understand headlines that the Clifford Chance report gives RBS a clean bill of health as their broader findings around the lack of fee transparency, lack of adherence to mandatory rules for internal valuations and need for an improvement in the business culture of GRG tally with the central themes of the Tomlinson Report and the patterns of behaviour I witnessed."

Clifford Chance declined to comment.

The report was originally due to be published in January, but – as revealed by Legal Week last month – faced delayed following difficulties in evidence collection.

Several businesses which passed on information to Tomlinson declined to forward evidence to CC, having previously encountered the firm as an adviser to the bank in restructuring litigation.

A source close to the matter said other businesses were nervous about forwarding commercially sensitive information to the magic circle firm, given its history of advising the bank.

In November, RBS stated that CC's instruction did not amount to a conflict of interest, despite the firm acting for the bank in various related restructuring and litigation matters.

Conceicao, who worked alongside partner Kelwin Nicholls on the matter, also referred volume matters related to the review to lawyers at TLT Solicitors and DMH Stallard, both of which bill at far cheaper rates.

The arrangement has allowed the bank to save more than half its initial budget for the investigation, according to one well-placed source.