A gangmaster is an individual or business that supplies labour to areas such as agriculture, horticulture, and food processing and packaging.
According to the GLA, Robert Taylor, director of Momentus, was keeping several workers in his care in cramped conditions, with uncertified electricity and gas provisions.
The authority also claims that Taylor was illegally paying the workers less than minimum wage for their work at companies in question.
British Bakeries manufactures bread under the Hovis, Mothers Pride and Nimble, while Thorntons and Florette are leading chocolate and bagged salad producers respectively.
Taylor has now had his license revoked, the GLA said.
The discovery highlights the importance of companies to remain vigilant and aware of their employees' situations, especially in the food industry, where there are over 30,000 foreign and migrant workers, according to the UK Food and Drink Federation.
"Yet again we see that the food on our plates on dinner tables across the UK could be there at the expense of exploited workers," said GLA chairman Paul Whitehouse.
He also said he is "determined" to stamp out worker abuse in the UK.
"Any group of workers who are dependent on consumer demand for a weekly job should at least expect to receive the minimum wage and the protection of UK law," he said.
Gangmaster Licensing Authority
The GLA was set up by the UK government to curb the exploitation of workers following the death of 23 Chinese cockle pickers in Morecambe Bay in 2005.
Anybody who supplies workers to the agriculture, shellfish gathering and food and drink processing and packaging sectors in the UK needs to be licensed by the GLA, or they risk prosecution and imprisonment of up to 10 years.
The GLA has been extremely vigilant in its crackdown on illegal practices, and in December the association uncovered inadequate safety standards and worker exploitation by three gangmasters operating in Worcestershire.
And last summer, the GLA revoked 13 licences held by labour providers to the food industry, for alleged illegal breaches of laws that protect workers.
EU measures The European Commission is also looking at implementing a similar crackdown on illegal labour practices, and has propose an EU-wide law that would expose food managers across the bloc to fines and possible jail time.
The Commission is also proposing an EU-wide requirement that all employers undertake specific checks before recruiting a third-country national and notify national regulators.
Under the requirements, member states would be required to pass laws imposing criminal penalties against those who have repeatedly infringed the law, who are caught employing a significant number of illegal labourers, who operate using exploitative working conditions, or if they know that the worker is a victim of human trafficking.