The Scottish government has accused supermarkets of “undermining the spirit” of its alcohol laws by selling cheap drinks.

Legislation banning volume sales of alcohol and certain multibuys came into force last year – but loopholes mean retailers can still offer discounts on internet sales made in England, while some multibuys continue to be legal.

Members of Holyrood’s health committee challenged representatives from Asda and Tesco on the issue during a session on the government’s plans to introduce minimum unit pricing.

SNP MSP Jim Eadie said multiple grocers had been accused of “undermining the spirit of the legislation” by “slashing prices and encouraging online purchasing”.

He said: “It does leave the impression … that your companies are putting their profits before the health of the people of Scotland.”

Labour MSP Richard Simpson said: “The spirit of the law was quite clear, that we wanted to ban discounting for volume, and yet the supermarkets particularly – and also the small stores – are still selling on a volume discounting basis.”

Under the new laws it is legal for shops to offer multibuys, as long as a single pack is not sold for more than it would be in the multibuy deal. For example, Asda cut the price of some single bottles of wine to £3.33 in order to be able to offer three-for-£9.99 deals.

Asda’s regional affairs head David Paterson said: “The clear intention of the quantity discount ban was to reduce any incentive for a customer to buy a larger amount of alcohol than they had intended to. That was the clear and unequivocal objective.

“We made it very clear particularly in the last Alcohol Bill that when you intervene in a market which is part of a wider UK single market, there are a number of unintended consequences and they cannot be wished away.

“So, in the same sense that I have seen attacks on other retailers about the use of online, it seems a bizarre situation to me that there are companies based solely in England that can continue to sell alcohol at whatever price they want but that in some sense companies that are in Scotland and invest here shouldn’t also be able to do that. There has to be a level playing field.”

He added: “I think it’s worth saying that we didn’t slash our prices and we haven’t driven customers online. We don’t have an online alcohol offering.”

Tesco’s government affairs director Emma Reynolds said: “In a competitive market, if you do want action on price, it needs to be government-led and through legislation because we are in the business of competing for the best possible offers for customers.”