Pubs tested in underage sting operations are subject to a postcode lottery. Councils are taking a very varied approach to underage sting operations, with some carrying out hundreds a year and others only a handful.
These are the findings of a survey of 68 of the 168 local authorities that are responsible for test purchase operations in England and Wales.
The survey, carried out by the Liberal Democrats, found a failure rate of 23% in all stings conducted in the two years to November 2006.
But it shows massive differences in the number of operations carried out by different councils.
For example, among county councils, Lancashire carried out 918 stings over the two years, while Northumberland had 95 and Herefordshire conducted just 34.
The number of tests at the London boroughs surveyed varied from 20 in Hounslow to 229 in Southwark.
Federation of Licensed Victuallers Associations chief executive Tony Payne said he had noticed the trend of some councils carrying out stings more readily than others.
"They are targeting certain pubs or off-licences where they expect it to happen," he said. "It shouldn't happen anyway, if staff are given proper training." The survey also shows a large variation in test purchase failure rates.
Three councils registered failure rates of less than 10%, with Bexley in London the lowest on 6%.
North Somerset topped the table with a 53% failure rate - although only 19 stings occurred there over the two years covered by the survey.
Liberal Democrat local government spokesman Andrew Stunell used the statistics on failure rates to call for pubs and shops to do more to curb underage sales. "It is high time that local pubs and off-licences made a new year's resolution to be much more careful about selling alcohol to teenagers and young people," he said.