West London-based Ramesh and Rama Parmar have accused the bank of deliberately concealing a complex facility called the "credit limit utilisation" when selling the product to them.
The facility locked the couple into a higher interest deal just as rates fell to their lowest level on record in the UK after the global financial crash.
Judge Andrew Hochhauser at the business and property court at the High Court in London would hear the case this week.
The bank in question contests the claim and has declined to comment.
Lawyers for the Parmars, Lex Law, will tell the judge that between 2006 and 2009 the bank "acted in its own interests" by "foisting entirely unsuitable interest rate swap products" on the couple.
The couple run a small family business of importing latex gloves from Malaysia used by doctors, dentists and medical clinics.
They had used the unnamed bank since 1970 to finance a property in Perivale, west London, which was the warehouse for the business.
He added that the bank "pestered" the couple for three years with multiple presentations promoting a hedging swap product.
It is also alleged that the bank misled the Parmars by telling them in 2008-09 that interest rates were likely to rise again even though, according to Akram, "the bank's own internal economic forecasters at the time were predicting that rates would go down".
If the legal action is successful, it could lead to thousands of small businesses bringing similar claims.
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