More than 100 people have submitted a claim for compensation after falling ill on a .
Lawyers representing the claimants say that there were "repeated outbreaks" onboard a ferry between April and June.
In May, 519 travellers experienced shortly after the ship set sail from for a two-week cruise.
The parent company Carnival had been accused of downplaying the matter by claiming that less than 1% of passengers had been affected.
But figures from port health authority show that the number was closer to 12%.
Passengers onboard previous sailings have said that problems with stomach bugs had occurred during their stays.
The spread appeared to begin around April 20, with 92 people taken ill on Ventura's 10-day cruise around Spain and Portugal.
More than 300 people -16% of passengers - were taken ill during its 19-night cruise to the Mediterranean, which departed Southampton on April 26.
And just under 12% of passengers reported symptoms on the following cruise - a three-night trip to Belgium on May 15.
Norovirus is a stomach bug that causes , and the germs cannot be killed with alcohol hand gel.
According to the , "it can be very unpleasant, but usually goes away in about two days."
Although the , very often, it can take up to a week for people to fully recover, meaning that for many, the bug ruined expensive holidays.
Hudgell Solicitors said it was working on behalf of 115 holidaymakers to seek compensation for "illness, loss of enjoyment and losses".
Anne Thomson, a lawyer at the firm, said it was "undeniable" that the illness had been rife on Ventura.
Ms Thomson said: "Let's not forget, it's not just the time people are confined to the cabin and are too ill to leave, but also the impact it has on the rest of their holiday, as it takes some time to recover from feeling so unwell to again fully enjoy the facilities, restaurants, and locations and days out."
A P&O spokesperson said: "We are sorry some of our guests may have been affected and we will be responding to the letter of claim in due course."
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