As chief medical officer Sir Liam Donaldson continued his crusade for potentially "devastating" minimum pricing levels on alcohol this week, new research revealed supermarkets and convenience stores were already leading the way on responsible retailing.

Supermarkets and convenience stores have upped their games when it comes to following proper protocol on underage sales, according to a new study carried out by test purchasing specialists Serve Legal.

Serve Legal carried out 14,620 sting operations in supermarkets, convenience stores, off-licences and pubs during 2008. Using 18-year-old subjects, it tested whether retailers were correctly checking young people for ID.

Overall the off-trade faired better by far, with an official pass rate of 66% compared with just 54% for pubs and clubs.

There was also a stark improvement in the grocery sector's performance. Supermarkets' pass rates soared from 60% in 2007 to 69%. Although convenience stores were not monitored the previous year, there was a noticeable improvement over the course of 2008. In the first quarter, c-stores' pass rate was 62%, but this rose to 66% in the final quarter.

Much of retailers' success came from switching from a Think 21 policy to Think 25. Stores had an 85% pass rate after raising the threshold, compared with 79% beforehand.

The results showed that grocers and in particular c-store operators were taking the issue of responsible retailing much more seriously, said Serve Legal director Charlie Mowat. "There is a broader focus on responsible retailing at management level, a better understanding of the law and better training for staff."

The results were welcomed by the British Retail Consortium as further evidence of the leadership retailers were providing on alcohol issues, making minimum pricing seem even more unnecessary.

"There is an irritating myth encapsulated in this phrase 'pocket money prices', which suggests there is somehow a link between prices and underage drinking," said a BRC spokesman. "Actually they are two entirely separate things. The way to prevent under 18s from buying alcohol is to be very, very rigorous in stores about asking for proof of age ."

He went on to claim there was no link between the price of alcohol and irresponsible consumption.

Despite the positive results, retailers would not be resting on their laurels, said Association of Convenience Stores chief executive James Lowman.

"The non-compliance rate is still too high and we cannot allow complacency to slip in," he said.

Sir Liam's proposals for a 50p per unit minimum price were rejected by the Prime Minister.