Sir, Your article on test-purchasing could give readers the impression that Usdaw only wants repeat ­offenders to be the subject of test purchases, but this is not the case ('Test purchasing 'should target ­repeat offenders', 7 May).

Many of our members feel the aim of test-purchasing is more often to catch out hardworking, law abiding shop workers rather than actually prevent underage sales. This situation helps nobody.

We want to see more consistency and transparency in test-purchasing. We think it could be better targeted at shops that are serial offenders, but that is because we think the process should be intelligence-led. We also want to see test-purchasing controlled by a binding code of practice, and we are pleased the Local Better Regulations Office has committed to drawing this up.

We want more resources devoted to dealing with purchasers, particularly to get the message across to young people. Our members are on the front line of policing age-restricted sales and Usdaw will campaign until they are free from fear of abuse or violence when asking for proof of age, and free from the fear of disciplinary action if they get a sale decision wrong.

John Hannett, general secretary, Usdaw