Clifford Chance (CC) is being investigated by the Solicitors Regulation Authority (SRA) over its controversial role in the long-running Excalibur case.

CC has turned to Clyde & Co for advice on the SRA investigation, which was reported earlier this morning by Financial News.

The firm has already faced significant scrutiny over its involvement in the $1.6bn case, which was brought by Excalibur Ventures, an aspiring oil exploration firm, against two US oil companies – Gulf Keystone Petroleum and Texas Keystone.

The claim was backed by a group of litigation funders, including the now disbanded BlackRobe Capital Partners, New York-based hedge fund Platinum Capital Partners and a UK entity called Psari Holdings, which was controlled by Greek shipping magnates Adonis and Filippos Lemos.

A 2013 High Court judgment found that the funders were liable for the defence costs of the two defendants, a ruling that was upheld by the Court of Appeal (CoA) last November.

CC was criticised by the CoA for its role advising Excalibur, after it emerged that there were family ties between CC's lead partner, Alex Panayides, and one of the litigation funders.

Panayides' father had been chairman of one of the Lemos family's ship management companies, while his brother was a "longstanding and trusted" employee of a Lemos family company.

In December 2015, it was reported that CC had settled a professional negligence claim by the Lemos family, who argued that CC had overstated the case's chance of success. The family put in £13.75m of funding.

While the SRA regularly investigates individual lawyers, it is less common for the watchdog to probe major law firms.

For example, the SRA referred three Clydes partners to the Solicitors Disciplinary Tribunal for breaching money laundering rules earlier this year. The trio were each fined £10,000.

News of CC's investigation comes after the firm posted double-digit increases in both revenue and profit per equity partner (PEP) yesterday (6 July), taking both metrics to new highs for the firm.

Turnover climbed 11% to £1.54bn, with PEP soaring by 12% to an average of £1.38m against almost static equity partner count.

CC, the SRA and Clyde & Co all declined to comment.