The Financial Conduct Authority (FCA) has said it is exploring whether it can take "further action" against the Royal Bank of Scotland (RBS) over allegations that the bank mistreated 12,000 small business customers.

The FCA published an interim summary of a review it commissioned into the actions of RBS's now-defunct Global Restructuring Group (GRG) on 23 October after being under political pressure to release the findings.

The review found evidence of "widespread inappropriate treatment" of small business customers, including failing to support businesses in a manner consistent with good turnaround practice.

It said it had identified instances of inappropriate treatment on the part of GRG in 92% of the cases it reviewed.

"RBS has accepted that it did not meet the standards it set for itself which impacted on how it treated some of its SME customers," FCA chief executive Andrew Bailey said.

"We are investigating the matters arising from the Skilled Person's Report and are focussing on whether there is any basis for further action within our powers. We cannot comment any further on this."

The interim summary released by the FCA said that over a third of the RBS small business customers transferred to GRG were not viable at the time of transfer and could be expected to face insolvency or administration regardless of the bank's actions.

It also said only 16% of the cases sampled displayed inappropriate action by GRG which "appeared likely to have caused material financial distress".

"Commercial lending activity is largely unregulated in the UK but given the seriousness of the allegations against RBS it was appropriate for us to look at their treatment of SME customers," Bailey added.

"While the most serious allegations were not upheld... the report did identify other concerns about the treatment of SME customers."

RBS welcomed the FCA's confirmation that the most serious allegations against the bank were not upheld.

"I am pleased that the regulator has confirmed the findings from last November and that the most serious allegations made against the bank have not been upheld," RBS chief executive Ross McEwan said.

"The culture, structure and way RBS operates today have all changed fundamentally since the period under review."