They are billed as the perfect holidays. You can escape from everyday life and relax with the promise of exotic destinations, stylish surroundings and silver service dining.

They are billed as the perfect holidays. You can escape from everyday life and relax with the promise of exotic destinations, stylish surroundings and silver service dining.

Yet despite the growing popularity of holidays on the ocean wave, being a passenger on a cruise liner may not be good for your health.

A record one million Britons booked a cruise last year, up 14 per cent on 2002 and double the number seven years ago. But reports of illness are rising. The Consumers' Association has found that one in six cruise passengers fall ill, compared with one in nine holidaymakers.

The main health problem, apart from food poisoning and broken limbs, is a communicable gastric illness.

In November last year, 500 passengers on the P&O liner Aurorawere struck down by a highly infectious norovirus which causes vomiting and diarrhoea. The captain was refused permission to dock in Greece, and Spain closed its borders with Gibraltar.

A spokeswoman for the Health Protection Agency said cruise ships offer the "ideal environment" for the spread of gastrointestinal illnesses.

She said: " Where people are living so closely together it is bound to strike from time to time. You see the same in schools, hospitals and hotels. Cruise ships have to have the mechanisms in place to deal with this efficiently. It's a question of scale. In schools or hospitals the potential is there to affect a greater number. On a ship the passengers are shut off from the greater population but the spread is obviously faster within the passenger community itself."

The Aurora has a chequered past. Some 100 passengers fell ill on the ship with the same norovirus in April last year in the Caribbean. It is unclear whether the outbreaks were related, but Health Protection Agency guidelines state that steam cleaning and quarantining can be necessary if there have been repeated outbreaks on a the same ship.

About 120 passengers who travelled on Aurora last year are seeking a combined total of more than £1m compensation from P&O.

They claim the operator did not do enough to stop the spread of the outbreak and that it failed to warn passengers on subsequent cruises of the ship's history.

Suki Chhokar, who is representing the passengers, condemned cruise liners as "floating prisons once an outbreak occurs". He said: "It would be unfair to say cruises are bad for your health, but our experience is that serious stomach illnesses like the norovirus are becoming more common and people are becoming more aware. That's why we're seeing an increase in reports."

Mr Chhokar said that the most common complaints he hears from cruise passengers include undercooked food, failure to clean swimming pools and cabins and unhelpful tour reps. He added: "Cruises are a lot more expensive and are often used to celebrate special occasions - honeymoons or retirement - and so people have high expectations."

Bryony Coulson, the manager of the industry group, the Passenger Shipping Association, said most people who went on cruises enjoyed their trips and experienced no difficulties and that passenger numbers were rising.

She said: "Our agents are quite surprised at how few complaints they receive, though people may have contacted P&O directly or claimed it on insurance."

A spokesman for Endsleigh Insurance said the company had not noted a disproportionate number of claims from those who had travelled on ocean liner holidays and that it did not differentiate between those travelling by cruise in its policy premiums. Fortis Insurance said it did not receive an unexpected number of complaints about cruise holidays, but that payouts were higher because of the expense incurred.

How being at sea spreads germs

Cruise liners are the ideal environment for the transmission and spread of stomach bugs such as norovirus. Large groups of people from different places congregate in a confined environment for weeks at a time, often stopping off for sightseeing visits on the way.

The bug is transmitted through person-to-person contact, predominantly via bacteria found in faeces, passed by infected hands and surfaces, or in contaminated food or water.

Hospitals, schools and hotels also provide favourable conditions for transmission to occur.

Norovirus has a high attack rate. More than half of those who come into contact with it will be affected. The sufferer faces up to 48 hours of nausea, projectile vomiting and watery diarrhoea. Discomfort can be extended if patients already suffer from conditions such as irritable bowel syndrome. The elderly or infirm are particularly susceptible.

The only way to tackle an outbreak is to identify the problem quickly so that control measures can be implemented. These include instruction in basic hygiene and food handling, prompt disinfection of contaminated areas and the isolation of affected crew members or passengers for 72 hours after clinical recovery.