UK-based Which? magazine found that of the 26 products tested, only Asda's Good For You roast chicken sandwich lived up to its label and contained 100 per cent chicken in its meat ingredient.
All the other brands failed to comply, instead pumping their products with a mix of oils, water and starch to bulk up the meat, and chicken stock, salt, sugar and flavourings to boost taste - taking advantage of FSA voluntary codes of practice.
The BHS department store sandwich had the most misleading label, which claimed to contain 100 per cent chicken breast. Yet on inspection the back label ingredients listed a mixture of water, glucose syrup, thickener, salt and salt compound.
And Marks and Spencers, who has a reputation for high-quality produce, was found to add salt, dextrose, stabilisers, starch and protein to the meat in its chicken and bacon sandwich.
Jaclyn Clarabut, who carried out the Which? investigation, said: "We want food companies to come clean, and spell out clearly on the front of packs exactly what shoppers are paying for. Are they paying for meat, or meat pumped up with water, preservatives and starch?
"Just one of the 26 chicken sandwiches we looked at had chicken that was 100 per cent chicken. Until the food industry adopts a better approach to labelling sandwiches, consumers are at risk of being misled."
But the problem lies with the current FSA discretionary code of practice, set up in 2003 following a similar investigation by a Shropshire-based trading standards officer.
The FSA attempted to get food manufacturers to sign up to the code, which states that added ingredients should be mentioned in the product name rather than just on the back of the pack, much like the regulations governing most other products.
But the food industry's reluctance to label their sandwiches honestly, for example 'chicken with added oil and flavourings', means that three years later the code is not adhered to.
A FSA spokesperson acknowledged "...there are issues to be resolved inrelation to how meat products in sandwiches are labelled in the name of thefood.
"LACORS (Local Authorities Co-ordinators of Regulatory Services) have recently asked us for advice on how to proceed on thisin development of a guidance document. The FSA is thereforefacilitating a meeting with LACORS and stakeholders shortly to discuss thisparticular issue. The aim is to hear the views of all the differentstakeholders. The Agency will then consider these views and formulateadvice for LACORS in order to find a way forward."
Which? confirms that a plan has been tabled which would allow only sandwiches containing 95 per cent meat or more to be called chicken sandwiches, but critics say this compromise sells the consumer short.
Jeanette Longfield, from food campaign group Sustain, told Which? magazine: "Over my dead body. It's either chicken or it's not. While there is no agreement the food industry can continue to sell rubbish."
The ongoing debate over nutritional labelling in the UK is being carried out against a backdrop of growing concern over health.
Equipping consumers with nutritional knowledge has become a key component of the battle to beat rising obesity, heart disease and diabetes rates.
Many sectors of the food industry have introduced their own signposting schemes in order to counter accusations that the industry has contributed to these epidemics, but while the chicken code of practice remains voluntary, critics worry that manufacturers are able to hoodwink the public.