A Glasgow businessman has revealed how the mis-selling by Royal Bank of Scotland of an interest-rate-hedging product five years ago has cost him £500,000.

Clayton Perks also said he was treated like a "prisoner of war" under the control of an RBS-appointed external adviser who it later emerged had no contract with the bank.

On Friday, the Financial Services Authority said the four big banks had agreed to review all sales of interest-rate-swap agreements (IRSAs) and compensate victims of mis-selling, just 48 hours after Barclays was hit by a seismic £290 million fine for manipulating inter-bank lending rates. State-owned RBS has admitted it is "cooperating with the investigations" into the latest scandal.

Now Perks, an Australian who founded Glasgow Chiropractic at St Vincent Place 15 years ago and has 17 clinics across the city, has become the first Scottish IRSA mis-selling victim to protest publicly about the bank he depended on for support.

He this week formally complained to RBS chief executive Stephen Hester about a catalogue of alleged misconduct by the bank, including a serious breach of data protection in installing an "independent adviser" to run his business for two years – then denying any connection with the adviser.

That followed a similar washing of hands for selling Perks the IRSA, despite the bank having proposed the agreement and then made it a condition of his continued financing in 2007. The case is typical of up to 28,000 small businesses that were approached by their banks between 2001 and 2008 and persuaded to sign up to what appeared to be a simple fixed-rate loan, to protect against rising interest rates. It was often a "swap" derivative, promoted by a salesman from the bank's financial-markets division who had a target to sell what were highly profitable products for the bank.

"We had said we didn't want to take the product, but the bank said 'your funding is dependent on you hedging the interest rate'," Perks told the Sunday Herald. "The message over and over at the time was 'you need to fix because rates are going up'."

But there was no discussion of the risk of rates falling. When they crashed to 0.5% three years ago, businesses were stuck on rates of about 6% instead of 3%, and those who were sold the most complex "structured collars" – which the FSA has said should never have been sold to small businesses – had to pay even higher rates. Everyone with a "swap" was saddled with a huge extra "exit fee" liability on the business, never disclosed and typically now up to 30% of the original loan.

When RBS crashed and was bailed out by the taxpayer in late 2008, Perks, like business borrowers everywhere, found himself summoned to a meeting. "The tone of the meeting was really hostile," he says. "The relationship manager didn't come – they were off with stress – and then we had six relationship managers in 18 months.

"I was told my business, which the bank had valued at £4m, was now worth zero, the bank was taking a 12.5% stake in it, and it would have to break the swap agreement in order to restructure my borrowings."

A second swap agreement was enforced, which was also later broken by the bank. The effect was to pile a total extra liability of £500,000 onto a business powerless to object.

RBS put the business into the bank's Global Restructuring Group (GRG) and later appointed an "independent adviser" to take control in St Vincent Place. "Once you are in GRG, you have to do it their way," Perks says. "He was overbearing at all times, but we did what we were told for two years. When I queried the hedging agreement, he told me, 'if you think you can do anything about it you are naive and delusional'."

After requesting on two occasions to see the adviser's professional rates and his letter of engagement from the bank, he was sent a non-itemised one-year bill for £10,000. "His lawyers told me he was not paid by the bank and had not been engaged by them. So for two-and-a-half years RBS was openly sharing all my information with an agent who had no contractual arrangement, and is now said to be nothing to do with them."

Perks has complained formally to chief executive Hester about the breach of data protection, while his mis-selling complaint will at last now be reviewed by the bank.

Senior managers have continued to be "aggressive", Perks says. "We are being bullied and harassed. At the last meeting I was told I was like a carnival performer doing the three-cup trick. All I am asking for is fairness."

Glasgow Chiropractic, which supports 70 jobs, covers all of its interest payments and has plenty of cash in the bank, but Perks is nevertheless concerned the bank plans to turn the screw again. It has accused him of being "in breach" of his lending agreements, triggering the bank's right to renegotiate or withdraw its support in three months' time.

"It is a fabricated breach," he says. "They have deliberately created a false situation. It is like a game where they continually change the rules, trying to get money out of surviving businesses to bolster their own balance sheet."

He concludes: "We have been trading here very successfully for 15 years, we are strong and profitable and we want to be here for the next 20 years. Without the hedges we would now be paying 3% and would have avoided the £500,000 bill.

"The problem is the [banking] culture doesn't seem to have changed. Banks are supposed to be helping small businesses, but I don't consider their actions helpful. Even though we have done all the right things, it feels like being a prisoner of war."

It was only when he read an investigation last month in The Herald that Perks complained to the bank about the mis-selling. "I thought I was the only one," he says. "Until now I have just been rolling with the punches, but when you find out there are thousands of cases you get to the stage where enough is enough, and you have to make a bit of noise."

A spokesman for RBS said: "We are committed to the fair and timely treatment of our customers and will work closely with the FSA to achieve that end."

He said the bank had rejected Perks's complaints and invited him to go to the Ombudsman.