Miss Challis, a supervisor for a care agency, told the Standard: “We went into Starbucks to get a coffee but before that mum needed to use the toilet.
“My mum loves their mugs, so was adding one to the mini-collection, and we wanted to sit down and have a drink because mum needed a rest.
“Both toilets were locked so I asked the lady is she wouldn’t mind opening them for me.
“She looked my mum up and down and said ‘she isn’t disabled.’
“Mum replied with ‘not every disability is visible.’
“From that she reluctantly opened the door, looked my mum up and down again, and said ‘you look perfectly fine to me.’
“To my utter shock I went over to ask to speak to the manager. He said he wasn’t going to deal with it, he didn’t even apologise.”
The manager told Miss Challis that English was not the staff member’s first language, but she said the pair felt this was “no excuse” and left the store.
She said; “From there we went to sit down and have a drink elsewhere and mum was very, very upset and felt humiliated.
“I was so upset; when my mum is upset I’m upset and she’s a very strong woman so seeing her break is heartbreaking for me.”
Miss Challis said the incident has put her off visiting Starbucks in future, telling the Standard: “I used to go there quite a bit, and I’ll never ever use them again – Costa all the way.”
A spokeswoman for Starbucks UK said: “We have investigated this matter and would like to pass on our apologies to the customer affected. Our toilets are always available for our customers use.”
Liz Sayce, chief executive of Disability Rights UK, said the incident highlighted the need for companies to be more aware of unseen disabilities.
She said: “There has been a legal obligation since 1999 to offer equal access to services to people with any form of disability.
“I’m glad that Starbucks has apologised, but we really need companies to make it clear to all their staff that they have a legal duty to make services accessible to people with any kind of disability.
“So often the public thinks that because the the person isn’t using a wheelchair they’re not really disabled.
“Disabilities like arthritis, diabetes, heart conditions are just as real.
“It can be very upsetting if you are not welcomed and a service is not made accessible to you.”