A former Scottish Government minister has compared Tesco's suspected treatment of suppliers to practices seen in Mafia movie The Godfather.

Groceries Code Adjudicator Christine Tacon was giving evidence to Holyrood's Rural Affairs Committee on the day that she announced that she is investigating indications of delayed payments, penalties and unaccounted-for deductions from suppliers by the supermarket giant.

She encouraged other suppliers to speak to her anonymously with any further allegations against Tesco or other retailers.

Representatives from Sainsbury's, Marks and Spencer and Lidl told the committee that such practices are new to them.

Committee member Mike Russell, who held several ministerial posts in Alex Salmond's SNP Government, said: "They were new to me too. I had only read about them and seen them in films like The Godfather.

"We heard from the Grocery Code Adjudicator this morning about her top five issues, which I have to say, having led a sheltered life, made my hair curl."

Liberal Democrat MSP Jim Hume said: "It sounds shocking, if it is allegedly true, of course."

Ms Tacon told the committee: "I'm not launching an investigation based on allegations - I am launching an investigation based on reasonable suspicion."

She added: "For future investigations, a really strong message I want to give to direct suppliers is - I do need more than being told something over a dinner, I do need information and evidence in order to trigger these."

She encouraged suppliers to come forward with evidence such as emails, contracts or witness statements.

"I have a legal duty to protect that anonymity of all suppliers involved, so any evidence that I legally require I need that, but it will never get out to the retailer," she said.

"I do encourage suppliers to talk to me."

Ms Tacon elaborated on some of the suspected practices going on at Tesco.

"Delays in payments is generally where the supplier has given the retailer goods, the retailer pays for them and then deducts from that invoice for various reasons.

"The issue that I am looking at is deductions which were not agreed by the supplier for promotions, in some cases duplicate deductions and even some deductions without any errors at all."

She added: "An area that is in my top five issues that I have been working on for 18 months is drop-and-drive, where people, particularly in the chilled chains, will deliver what they believe to be 100,000 units to a retailer depot.

"They get no proof of delivery, they send an invoice for 100,000 and what they get back is an invoice for the 100,000 less 20,000 which the retailer said wasn't on the lorry."

James Bailey, business unit director for packaged goods at Sainsbury's, said such practices are "against the code of practice so we go to strenuous efforts not to breach that code of practice".

"They're not practices we recognise," he said.

Tom Hind, agriculture director at Tesco, said: "I'm not in a position to comment, given my area of the business."