Licensees are risking their lives by buying cellar gas cylinders from "cowboy" suppliers.
While there is never any shortage of suppliers willing to undercut the big operators in the field, the British Compressed Gases Association (BCGA) confirmed that there has been an increase over recent months in the number of cases of bogus refilled gas cylinders carrying the names of major suppliers.
Pubs think they are getting a bargain when offered big-brand supplies deals on the cheap.
However, while the cylinders may bear the names of companies such as BOC or Messer & Cryoservice, they have been obtained and refilled by rogue operators.
At best, beer quality will suffer if the gas mix is wrong. At worst, faulty or badly-filled cylinders could leak slowly, creating the danger of asphyxiation - or even explode.
A spokesman for the BCGA said: "This practice is nothing new, but it seems to be on the increase. We have to keep reminding pubs of the potential dangers."
Under health and safety regulations, pubs have a responsibility to carry out a risk assessment on their cellar practice.
In the event of an insurance claim, an "under-the-counter" deal to buy cheap gas could create serious problems for a publican. The British Beer & Pub Association (BBPA) has produced a guidance booklet, endorsed by the Health and Safety Executive, to help licensees assess the level of risk posed by an accidental release of CO2.
The BBPA has also collaborated with the BCGA to produce a Purchasing Guide for Gas Cylinders, a booklet which provides clear advice on ensuring that gases for drinks dispense meet the minimum quality and safety standards.
The BCGA Purchasing Guide and more information can be found on the association's website www.bcga.co.uk.