Last week, the Financial Conduct Authority fined the lender £8.9m for increasing borrowers’ monthly mortgage repayments to penalise it for its own uncorrected internal errors.

However, it seems the bank’s attempt to offer speedy redress in the wake of the fine led to some customers receiving a second compensation payment some years later.

According to The Telegraph, Clydesdale borrower Stan Semple took his case to the Financial Ombudsman Service (FOS) in 2010 and won. The bank subsequently wrote off the capital shortfall.

He said: “I’ve got a letter from them today saying they are writing off the shortfall amount and my mortgage has been credited with the amount. They can’t even correct their errors properly.

“How many other folk who took them to the FOS will also be told they are getting money credited to their mortgage – again?

“Now I’ve got the hassle of contacting them and trying to explain to them that I can’t take their money as I already got it three years ago.”

The FOS initially received roughly 600 complaints about the Clydesdale decision to adjust borrowers’ mortgage repayments, the majority of which were upheld in the customers’ favour.

A Clydesdale spokesman said: “There are a small number of cases where previous complaints may not have been taken into account and we’re contacting these customers to apologise for any inconvenience and to confirm the exact standing of their account.”

In 2009, Clydesdale discovered it had asked for incorrect mortgage repayments from 42,500 variable rate borrowers. As a result, roughly 22,000 customers made repayments insufficient to repay their mortgage by the end of the agreed terms.

These customers then faced unexpected increases in their monthly repayments to correct the error. After receiving the fine from the regulator, the lender promised to compensate 14,000 customers within 48 hours and to contact borrowers with more complex cases by October.