Lauren Lunn Farrow, 29, ordered the chicken burger with chips while out to lunch with a friend at Metropolitan Pub Company site the Merchant in Battersea, south-west London.
She said: “I just ordered and when it arrived I went to cut into it – [the glass] was between the chicken burger, then it had sauce over it and salad on top.
“I went up and alerted them to it and was really shocked. If I hadn’t cut into it I would have bitten into it and god knows what could have happened.”
The shard was approximately two square inches wide, she said, and looked like it had come from the bottom of a pint glass. "In the picture I took that's not the whole bit of glass," she said. "That's roughly a third of it sticking out.
“The manager was quite shocked and said that he would comp our meal and give us a few free drinks. He went into the kitchen and when he came back I asked if I could keep [the shard] and he said no, so I don’t know where it is now,” she added.
“I have no idea how it happened. It’s really scary because there were quite a lot of kids in there as well.”
The Merchant currently holds a five-star food-hygiene rating.
A spokesperson for the pub said: “Food safety is our top priority and we apologise unreservedly for this completely unacceptable and isolated lapse in our usually very high standards.
“As soon as this was brought to our attention we launched a full investigation into how this could have happened and have already taken appropriate action to ensure something like this never happens again.”