Mr Thurso said he was worried about the lack of information held by the Confederation of British Industry and the Federation of Small Businesses on embedded interest rate swaps.
Banks have paid out £306.3 million to firms that bought swaps sold independently as a way of offering protection against rising interest rates. But embedded swaps are excluded from a review by the Financial Conduct Authority because they are classed as commercial loans, which are not regulated.
At a hearing of the Treasury Select Committee, Mr Thurso told representatives of the CBI and FSB: "You are here to represent business. You do not know the size of the problem. You do not know who is regulating it."
The MP for Caithness, Sutherland and Easter Ross added: "These were products routinely sold, perhaps mis-sold, to companies without the expertise to unpick a vanilla swap let alone an embedded swap.
"It worries me that the representative of business is unaware of the scale of the problem."
Treasury Select Committee chairman Andrew Tyrie said business groups were previously slow to raise the broader issue of interest rate swap mis-selling. He said: "The important thing here is to discover whether we are dealing with a sizeable problem or not."
Priyen Patel, senior policy adviser at the Federation of Small Businesses, told the committee it became aware of the issue in December and was considering representations made to it. He said: "We are trying to figure out whether it is a market-wide problem. There is a consensus emerging that it is."
He said any "super-complaint" brought by the body over the products, also know as tailored business loans, would be a "long laborious process".
The exchange came in an evidence session for a Treasury committee investigation into the small business lending market.
Russel Griggs, the former Scottish Enterprise executive who is the external reviewer for the Banking Taskforce's appeal process established by the industry, played down conflict between small firms and banks.
He said: "I am probably of an age when I can remember disputes between SMEs (small and medium-sized enterprises) and banks have been going on decades. This is not something that has happened since 2008."
Professor Griggs, whose role is to ensure the appeals
process is independent when a firm disputes a bank's credit decision, said he had seen no evidence of "vindictive" behaviour towards firms.
However, he said this did not mean he disputed a report by Government adviser Lawrence Tomlinson that was highly critical of lending practices at Royal Bank of Scotland.
British Bankers' Association figures published yesterday showed net lending to firms fell £317m in January. This followed drops of £920m in December and £2 billion in November.
Mr Patel said firms still highlighted access to credit and the cost of credit among their greatest challenges. But Matthew Fell, director for competitive markets at the CBI, said: "I do not think the situation is going to continue as it has for the past five years."
Banks have improved their balance sheets, he said.
"Their appetite for lending is on the increase," he added.