The Office of Fair Trading's chairman, Philip Collins, yesterday defended the OFT's offer of £100,000 payments to "whistleblowers" who pass on inside company information about illegal cartels.

Collins, hosting a series of briefings marking the first year of the OFT's Scottish office, said the "financial incentives" were aimed at "staff working in businesses who are aware if something illegal going on".

He went on: "I don't suppose we expect to offer that (£100,000) on many occasions, but we have already had a number of interesting calls."

The OFT's Scottish representative, Kyla Brand, added: "The OFT in Scotland welcomes constant intelligence and information to ensure we remain fully informed of issues that are affecting Scotland."

The initiative, launched earlier this month, was attacked by some competition lawyers as "a bribe for snitches" and "big brother tactics". But Collins said: "This is a novel policy for cartel authorities but it is a common practice in law enforcement generally."

The appeal to expose price-fixing applies not only to big corporates but to public sector contracts.

The OFT said it had in the past year saved Scottish consumers £6m through investigating price-fixing, £4m through addressing competition concerns following mergers, and £1m through tackling scams such as fake lotteries, prize draws or psychic scams.

It works alongside the Trading Standards Service and Consumer Direct Scotland, the hotline which has taken over 300,000 calls since inception. One call in five is referred on to trading standards for possible enforcement, and the average saving to complainants is £100.

"It is the first tier of consumer advice and, hopefully, helps to inform consumers what their rights are,"Collins said. He said Scotland's contact centre in Lewis was the best-performing in the UK, with a customer satisfaction rate of 91%.

Collins said the OFT, under attack in some quarters for its more aggressive approach to big business and huge increases in fines, was not just interested in the "headline stuff" of enforcement.

"If you engage actively with business you can often bring about changes in behaviour which are beneficial to the market. The clearest case in the last year or so has been inclusive pricing of air fares."

No-frills airlines had been forced to present their prices in a common format inclusive of taxes, charges and extras, under pressure from the OFT "with enforcement powers in the background", Collins said.

The OFT had also made it possible for borrowers properly to compare credit card charges, by persuading banks to adopt a common definition of APR, and had brought a test case against the banks involving the legality of overdraft charges.

But on whether it would pursue US-owned lender Egg over its unilateral closure of customer credit card accounts (many of them in credit and simply unprofitable), Collins said he could act only in the case of illegality. "All we can say is we are in dialogue."

On payment protection insurance, where the banks are under fire for making huge profits from inflated premiums, the OFT has uncovered that only 20% of the money collected in premiums is paid out in claims - but it has been forced to refer the whole issue to the Competition Commission.

Collins commented: "It would be nice to have got a voluntary solution on PPI. It is a very complex market with a lot of players."