Convenience stores have caught up with supermarkets in correctly enforcing ID checks for age-restricted products, with a 77% pass rate in tests carried out last year, according to the results of a new survey seen exclusively by The Grocer.

But while headway was being made in challenging customers for ID across the board, factors such as time of day, day of the week, products purchased, age and even the gender of the server continue to have an undue influence, test purchasing company Serve Legal found.

Serve Legal carried out more than 30,000 visits to a range of retailers using 1,500 18 or 19-year-old testers during 2010, and recorded how many retailers challenged them for ID when they bought restricted products a legal obligation if they appear to be younger than 21 or 25.

Serve Legal found one of the most significant fluctuations was caused by the age of the server.

Those in their 30s, 40s and 50s all recorded a 78% pass rate, but servers aged 19 or under only achieved a 70% pass rate, possibly because they lacked the confidence to challenge their peers, the survey suggested. The survey also found that female servers were more diligent in challenging customers for ID than males.

Female servers recorded a 77% pass rate compared with 70% in males. There was also a significant variety in results based on what time of day a sale was made, with a drop-off in the evening suggesting servers become less thorough when they are busier.

"In the past, convenience stores have been seen as weak links by authorities and customers," said Serve Legal director Charlie Mowat.

"They've got fewer resources to spend on training and they got onto the issue a little bit behind ­supermarkets."

Mowat added that while discrepancies were caused by a variety of factors in ­individual cases, there were also large deviations between different regions, with Scotland as a whole recording a much higher pass rate than most English regions despite widespread concerns north of the border about binge drinking.

The poor performance of many English regions, he added, was down to a lack of consistency by different local authorities in the way they enforced the law and supported ­retailers.

Brandon Cook, Trading Standards Institute lead officer for age-restricted sales, said: "It's about the resources that local authorities can put into this. It comes down to local politicians and where their priorities lie. With cuts taking place it could become even worse in terms of consistency. It could mean that there's less support for business advice and ­training."

But he added that age-restricted products were still a "high priority" for local authorities. "I hope that it's one of the areas of legislation that won't be touched by cuts," he added.