Over 200 holidaymakers are suing Butlins after suffering a gastric illness while staying at the Bognor Regis resort between May and July 2011.
The 215 complainants are being represented by law firm Irwin Mitchell, and claim they fell ill with severe sickness, stomach cramps and diarrhoea as a result of sub-standard conditions.
They allege that the food was undercooked and left uncovered, as well as flies and pigeons being seen on and around food; lack of cleanliness in rooms and communal areas; sewage smells around the resort; and that the swimming pool was cloudy with slime around the edges.
Alison Hill, 55, a group leader of Mencap Hillingdon North, visited the site for five days in June 2011 with seven other volunteers and the group's 21 members.
Speaking to the Daily Mail, the carer said: "When one of our group members became ill I complained to the resort staff, but was then seen privately by a manager who asked me not to tell other guests about the illness and also asked if the party could leave early.
"We were stunned. Having to return earlier than planned caused major disruption, as day-to-day carers for some of our members were on holiday themselves and did not expect us to be returning early.
"Over two years on, we have still not been on another overnight visit as a group simply because we all do not want to go through the emotional and physical distress again."
At the time, Butlins put the illness down to being a "common 24-hour bug", with a spokesperson telling the BBC: "All guests at Bognor Regis who reported they had the virus have now left the resort.
"Our cleaning and sanitising procedures were successful in containing the spread of this common 24-hour bug with about 200 people affected out of 5,000 guests."
And the holiday company maintains it has upheld the highest standards of health and safety.
According to Travel Mole, a spokesman for Butlins Bognor Regis said: "We will robustly defend this speculative action raised at the High Court in Birmingham. We operate our resorts to the highest health and safety standards and work closely with the Health and Safety Executive to ensure that our guests' safety takes priority.
"Our standards of cleanliness and hygiene are recognised throughout the tourist industry world-wide. Such is our reputation on health issues that environmental officers from around the UK have described our policies and procedure as outstanding."
"[Butlins' parent] Bourne Leisure Ltd has denied liability and as such our clients have been left with no other option than to issue court proceedings as they seek justice for their ruined holidays."
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200 holidaymakers suing Butlins over illness from 'undercooked food'
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