Influential Scottish MP John Thurso has asked the new Financial Conduct Authority (FCA) to look at Clydesdale Bank's review of small business loans.

The Liberal Democrat former peer, who led the Government's recent inquiry into the banking system and is a long-standing member of the Treasury Select Committee, has written to Martin Wheatley, who becomes chief executive of the FCA on Monday.

It follows a Commons speech this week by Welsh LibDem MP Mark Williams that stepped up the pressure on Clydesdale and Yorkshire banks to reverse their decision to exclude their most widely-sold loan from the review of possible swap-related mis-selling.

Clydesdale has already been embarrassed by Dundee West Labour MP John McGovern, who secured from Treasury minister Greg Clark a Commons assurance that his constituent's fixed-rate tailored business loan (TBL) would be included in the review, an assurance then repudiated by the bank.

The Australian-owned banks responded to the growing pressure last week by explaining individual fixed-rate TBLs were not linked to identifiable derivatives or swaps. Experts, however, argue the loans have breakage fees linked to a derivative-based calculation, and the same argument applies to other types of TBL, which are included in the review.

Mr Thurso has told Mr Wheatley that since being told by the outgoing Financial Services Authority (FSA) that his constituent's TBL is a commercial loan, and therefore outwith its jurisdiction, he has been inundated with more cases.

He wrote: "There is a regular pattern. In good times prior to the crash, they were met in person by a manager who insisted they needed to protect themselves against interest- rate rises and put considerable pressure on them to purchase those products."

The MP added: "From the cases I have looked at there would appear to be a marked similarity with the selling of Libor swaps and indeed some clear parallels with PPI."

He said that following the exchange between Mr McGovern and Mr Clark, "it would appear there is some confusion as to what is actually being reviewed".

Clydesdale Bank says breakage fees are fully explained to customers, who are also advised to seek independent advice and who can still complain to the bank and the ombudsman.