Britain has been hit hardest by a major salmonella outbreak that has left more than 340 people across Europe ill – as investigators revealed chicken products as well as eggs could be responsible.

At least 207 cases have been recorded in the UK, more than any of the six other countries affected, with one person dying.

According to the European Centre for Disease Prevention and Control (ECDC), there have also been 106 reported cases in the Netherlands, 15 in Belgium, six in Germany, four in France, two in Austria and one in Denmark.

At least 34 people across the seven-country outbreak have had to go to hospital, with those infected ranging in age from less than one year old to 90.

Imported eggs served in restaurants and cafes are suspected as a major source of the outbreak in Britain, although health officials say the exact cause has not yet been established.

But European health officials are also investigating chicken products as a potential source after a small number of patients in the Netherlands reported eating chicken meat.

Experts have warned more cases are expected until proper control measures are put in place.

Will Raw, chair of the NFU's national poultry board, said it was 'hugely concerning' that eggs from abroad were being linked to a serious outbreak in the UK, adding: 'Food produced to standards that would be illegal in the UK is still being allowed into our market.

'This simply cannot be allowed to continue. Government must ensure at a minimum that adequate checks are being conducted on imports to ensure all food coming into the country is safe.'

Salmonella infections are caused by bacteria commonly found in the digestive tracts of animals and can be contracted by eating contaminated foods, particularly meat, poultry and eggs.

Previous outbreaks in the UK have also been linked to foods including salad leaves, cucumbers and chocolate.

The bacteria can also be spread through contaminated water, contact with infected animals or people and poor food hygiene.

It causes an infection of the gut known as gastroenteritis, with symptoms including diarrhoea, stomach cramps, vomiting and fever, as well as fatigue and muscle aches.

Symptoms usually develop within hours or days of infection and most people recover without treatment.

However, in severe cases the bacteria can spread beyond the gut and into the bloodstream, potentially requiring hospital treatment and antibiotics.

Young children, older people, pregnant women and those with weakened immune systems are at greater risk of becoming seriously ill.

Investigations in Britain have identified imported eggs as a potential source, with many of those thought to be affected having eaten eggs in restaurants or cafes.

Commercial laying hens producing British Lion eggs are vaccinated against Salmonella Enteritidis, the strain behind the current outbreak, which significantly reduces the risk of contamination.

Health officials have stressed there is currently no evidence that UK-produced eggs are affected.

Meanwhile, the Netherlands recorded a peak in cases in August and September last year.

Investigators there found a small number of patients had eaten chicken meat before becoming ill, raising the possibility that poultry products could also be involved in the wider European outbreak.

The strain involved was also behind a previous outbreak in the Netherlands, where eggs and poultry were suspected but no definitive source was found.

Last year the Dutch National Institute for Public Health and the Environment (RIVM) investigated 80 cases linked to the strain. After a period with no new infections, cases began appearing again this year and the investigation was reopened in July.

In the UK, 199 cases have been confirmed in England, six in Scotland and one each in Wales and Northern Ireland.

More than a third of patients for whom information was available required hospital treatment, while two developed potentially life-threatening infections after the bacteria spread to their bloodstream.

UK Health Security Agency (UKHSA) investigators have identified five unnamed food businesses linked to patients, with at least two visited by multiple people in the week before they became ill.

Jacquelyn McCormick, head of incidents at the Food Standards Agency, said: 'The exact cause has not yet been identified, however investigations so far have identified links to eggs imported from outside the UK, mainly used by food service and catering establishments such as restaurants or cafes, as a potential source.'

Officials have stressed there is no evidence that UK-produced eggs are affected.

However, people at greater risk of becoming seriously ill – including those over 65, children under five, pregnant women and people with weakened immune systems – have been advised to avoid raw or lightly cooked eggs and foods containing them when eating in cafes, restaurants and takeaways, unless they can be sure the eggs meet recognised UK safety standards.

Egg imports into Britain have risen sharply in recent years amid pressure on domestic supplies, with concerns repeatedly raised by British farmers about differences between UK and overseas production standards.

Imports from Ukraine have also increased significantly, prompting criticism from farming groups over production methods, including the use of conventional battery cages, which are banned in the UK.

But officials have not identified the country of origin of the eggs suspected in the current outbreak and there is no evidence linking Ukrainian eggs to the infections.

The investigation into the source of the outbreak is continuing.