Test purchasing was carried out by Trading Standards and the police at seven off-licences as part of Operation Cleansweep, with staff at four shops failing to ask teenagers under the age of 18 for identification.
The result follows numerous campaigns, both nationally and locally, warning staff at off-licences, pubs and supermarkets that they will face fines if they supply young people with alcohol.
Neighbourhood policing sergeant Nicki Bignell said: "I was disappointed, especially when we have been working hard to combat underage drinking and have been working with off-licences to increase ID checking.
"It is surprising that in this day and age, with so much media attention on the issue, that some off-licences are not asking for ID and questioning individuals when they look younger.
"On previous occasions, staff have been a little bit more switched on, but this time we had been given information by the community that there had been kids with alcohol in these areas. We had received reports of anti-social behaviour in the locations of certain off-licences."
Sgt Bignell was also shocked by the number of motoring offences recorded by traffic police during the week-long operation.
51 drivers will face prosecution for speeding, while 31 drivers were given fixed penalty notices for using their mobile phones or failing to use their seat belts.
Sgt Bignell continued: "Lots of people said they didn't wear their seat belts because they are safe drivers. But when there are 51 people speeding on the roads, all it takes is one of them to lose control of their vehicle and another life is lost.
"One person who was stopped even said 'This is Garstang, we don't wear seat belts.' We attend so many road collisions and the results of this operation just show that more needs to be done to educate drivers in the future."
Other results of the operation included:
- 4 prosecutions for no TV licences.
- 2 arrests for possession of drugs.
- 5 endorsable fixed penalty notices for motoring offences, which include licence points.
- 17 prohibition notices served on vehicles for illegal parts.
- 3 enquiries made to the Department of Welfare and Pensions for benefit fraud.
- 1 summons for driving with no insurance.
- 1 vehicle removed from the road.
- 4 on the spot £500 fines for illegal use of red diesel.
- 122 community questionnaires completed.
- 66 home fire checks requested.
Litter picks took place with the help of children from local schools, and dog fouling patrols were carried out by the Environment Agency. School truancy officers also came on board to track down wayward students.
Operation Cleansweep, which involved many different organisations, local councillors and members of the public, followed April's Operation Market, a one-day campaign which involved gathering intelligence from the public on various community issues.
Sgt Bignell said: "I believe we have had a very successful year and have made a huge impact on issues in the Garstang area, particularly on anti-social behaviour on a grass roots level.
"This operation allowed us to address problems that we had not yet dealt with and now it will help the police and all the partner agencies to prepare for the future and respond to the needs of the community."