GRAPHIC CONTENT WARNING: Some readers may find the video unpleasant to watch
Disgusted shopper Louis Yssel said he was left feeling sick after watching several of theÂ bright red, one and a half inch worms slither out of a piece of monkfish as he prepared a curry.
He said: 'It was absolutely disgusting. We were just preparing a meal and these worms began crawling out of the fish. It made me feel physically sick.'
Louis, 32 and partner Christopher Jones had bought the monkish tails from the fresh fish counter at the supermarket giant's Woodfield Plantation store on Sunday afternoon to make a fish and prawn curry later that day.
After returning to their Bawtry home from their shopping trip, the pair left the fish to marinade in a sauce of lemon and various herbs and spices prior to cooking it that evening.
Explained Louis: 'We marinaded it and then put it back in the fridge. It must only have been a few hours between buying it and using it.'
But as they took the fish from the fridge to put into the curry, the pair noticed the worms crawling out of the flesh.
He said: 'It was shocking '“Â pretty disgusting stuff. They were crawling out of the fish right in front of us. A few minutes later and they would have been in the pan without us noticing.
'I had already cookedÂ the bone from the fish to make a stock and we'd been tasting it as it went along, so we felt pretty sick knowing that we'dÂ already eaten some of it.'
The couple then contacted Tesco '“Â and they say they were offered a Â£7.50 refund for the monkfishÂ as well as a Â£10 voucher as way of an apology.
After refusing, Mr Yssel returned the fish to the supermarket where he says they were given a refund of Â£57 '“Â the total cost of their shopping bill.
He said: 'We received a half-hearted apology and the staff didn't appear to know what they were doing.'
The pair also say they were told that the supermarket would carry out an investigation and the couple are now demanding urgent answers after discovering that the worms might be parasitic and which if swallowed,Â can causeÂ severe abdominal pain, malnutrition, and vomiting.
It is thought the creatures might be anisakis worms which can be found in raw and uncooked fish.
Within a few hours of ingestion, the parasitic worm tries to burrow though the intestinal wall, but since it cannot penetrate it, it gets stuck and dies.
Its presence can then spark serious stomach cramps and vomiting and in some cases the worms have to be removed through surgery.
Added Mr Yssel: 'What if a child had eaten it?
'We tasted the curry sauce which already had fish in it and we are both pretty disgusted. It put us off eating that night because we felt sick and to be honest, it has put us off having fish and also shopping at Tesco again.'
We have contacted Tesco for a response.