Scotland's police forces can, from today, use youngsters to catch licensed traders selling alcohol to under-18s.

The roll-out of the test purchasing scheme, piloted in Fife for almost a year, is the first major national change in Scotland's licensing law in over a quarter of a century.

However, it is unlikely that any force will take up the option until later this summer.

All forces are expected to use "intelligence-led" stings rather than the more random approach deployed in Fife.

But the high failure rate in Fife and the readiness of licensing boards to close sources that have been caught out has raised concerns that thousands of Scottish retailers could have their livelihoods threatened.

The Scottish Grocers' Federation has even warned its members that the roll-out of test purchasing is a much greater threat to their survival than the growth of the supermarket chains.

By mid-March, 847 tests had been carried out in Fife, where licensing boards have operated a "two strikes and you're out" approach. In the campaign, 73 pubs and nightclubs and 71 off-licences were caught, a failure rate of 17%. All 144 have been reported to the procurator-fiscal. The number of prosecutions being processed is believed to be in single figures.

On second visits, just six failed, leading to five suspensions, although at least two, a Co-op and a BP filling station, are appealing the sanctions. One case is still pending A similar, non-statutory, scheme in the south side of Glasgow three years ago found that 33% of off-licences were selling to under-age customers.

Now, while insisting that licencees who put profit before social responsibility should be punished, lawyers, retailers and bar owners believe there will be a huge increase in the number of suspension hearings before Scotland's licensing boards.

Gordon Macrae, of the Scottish Grocers' Federation, said no retailer disagreed with the test purchasing concept but they were fearful of the way it could be implemented and called for a national proof-of-age scheme.

He added: "When rolled out we want it to be flexible enough to support retailers to put the right systems in place. Two strikes and out doesn't do that. Retailers could be have licences suspended through no fault of the company.

"It's such a serious issue many firms have made unintentional selling to under age customers a gross misconduct offence."

Some lawyers also claim that the sanctions handed out by licensing boards may be disproportionate to the offence, especially as the onus of proof is much less than in a courtroom.

Fife-based licensing law specialist Tom Johnston, speaking at a major conference in Glasgow last week, said there had been one prosecution where a licence holder was fined £225 in court, a much lesser sum than loss of livelihood for three or four months, which a licensing board can and has imposed.

Mr Johnston said: "Since the Fife licensing boards have been so compliant in agreeing with the police view, virtually no prosecutions have taken place.

"In essence the police feel they are getting a result' without the inconvenience of having to commit time and manpower to the due process of law."

Glasgow-based lawyer Jack Cummins added: "The experience of Fife and Glasgow some years back leaves me in no doubt that many licensed premises will be in front of licensing boards as a result and in serious trouble."

Some details of the approach to be taken by different forces remain to be ironed out, while teenage test purchasers have yet to be recruited in most areas.

Despite the criticisms, officers working with liquor licensing will relish having the tool in their armoury.

John Farrell, head of licensing at Strathclyde Police, said: "This is an operational tool we will certainly be using in our fight to ensure the well-being of communities."

An Executive spokeswoman said she could confirm the roll-out date but because of the election was unable to comment further.