A Waitrose & Partners spokesman said it worked with a number of charities to provide work experience and was “well experienced in making reasonable adjustments to help people succeed at work”.
“We are sorry to hear of Tom’s story and whilst we cannot comment on individual cases, we are investigating as a priority,” he said.
Ms Boyd said his placement was stopped when the firm’s head office was asked about the possibility of paid work.
She said she was told it was because he “couldn’t perform the whole role”.
“He deserved better,” she added.
“He deserved kindness, respect and the chance for all his hard work to mean something.
“No-one should be made to feel their contribution doesn’t matter, especially someone who’s given so much of themselves for so long.”
Volunteers do not have the same rights as an employee or worker, according to the government, external, though there are expectations for those undertaking vocational training.
The guidance states that those who volunteer should usually get a volunteer agreement that sets out the level of supervision and support they will receive.
It should also include advice on training and whether they were covered by the organisation’s insurance, as well as information about expenses and health and safety issues.
However, the agreements are not compulsory and do not form a contract.
Ms Boyd said she wanted to see legal protections like those afforded to employees by the Equality Act to extend to volunteers to ensure they have “rights and opportunities”.
“They can be terminated at any time and that’s not really the way we should be moving forward in society today,” she added.