A mother was left feeling humiliated after eating part of what she thought was KFC's new vegan burger, only to discover she had been served chicken.

Vanessa Franco, who recently turned vegan and has been a life-long vegetarian, went through the drive-thru section of the Colliers Wood branch on Wednesday wanting to try out the fast-food giant's new burger.

But three bites in she knew something wasn't right.

"I realised the texture tasted different," the Pollards Hill woman told the Wimbledon Times.

"I drove back to KFC and asked them to confirm it was a vegan burger. That’s when the girl who served me told me it was a chicken fillet burger.

"She then called her colleague who told me to come inside.

"She also said if I took bites out of it then why didn’t I notice it was a chicken burger. I explained I have been a vegetarian my whole life."

With her baby asleep in the back seat of the car, Vanessa wanted to carry on the conversation in the drive-thru.

But she says staff insisted she come inside instead.

"I then went in with him and had to wake him up, the manager then came out," she added.

"That’s when he gave me a vegan burger, didn’t apologise and laughed and said 'you should of known it was chicken'.

"All of the staff stood there staring at me. I felt humiliated and have been left traumatised due to not only a life style choice but also religion being broken and made fun of.

"I was speechless and can't express how disgusting their customer service was."

A KFC spokesman admitted that how the situation played out was less than ideal.

“This isn’t great and we’re really sorry for what happened here," the spokesman said.

"Our vegan burger launched last month and we took its arrival seriously – putting strict new processes in place to make sure it’s served properly, including the use of separate coloured tongs and storage units.

"We’re following up with the team to remind them of the importance of getting this right and will be offering the guest a free meal on us to put things right.”

But if the second burger Vanessa was given that Wednesday is any indication, then she might not be in for a treat.

"The replacement burger wasn’t even cooked properly," she finished.

"The inside had cold patches amongst really hot bits."