The business action group attempting litigation against Royal Bank of Scotland in relation to its Global Restructuring Group has changed its legal advisers for the second time.

The RBS GRG Business Action Group has now appointed Enyo Law, having previously hired London-based Clyde & Co and then US firm Quinn Emanuel.

The group says its case will allege an "unlawful means conspiracy" by RBS-GRG against its customers and by several of its senior executives.

The individuals are understood to be chairman Sir Philip Hampton, former deputy chief executive Chris Sullivan, Derek Sach the head of GRG, and Aubrey Adams, head of property and responsible for West Register, the RBS subsidiary that bought distressed customer assets.

Litigation specialist Enyo Law says it is "not bound by conflicts that affect the majority of City law firms" and can act against major financial institutions.

The group said last autumn it hoped to register at least 600 claims in preparing a group litigation.

Its previous lawyers wrote to the bank last October protesting at the potential loss of evidence through the bank's planned closure of the GRG, which came under the Treasury Committee spotlight following the Tomlinson report. Former government adviser Lawrence Tomlinson reported that the GRG engineered customer defaults by procuring depressed valuations, and pushed firms into bankruptcy by levying excessive fees and charges, enabling West Register to pick up assets at knockdown prices.

A counter-report by RBS lawyers Clifford Chance rejected the central allegations. Mr Tomlinson, a millionaire businessman and RBS customer for 20 years, revealed last November that the bank had subsequently cancelled all his business and personal accounts.

The bank has declined to comment on the action.