Three British nationals in the UK have been infected with E.coli linked to the German outbreak, the Health Protection Agency said.
It brings the total number of cases in the UK to seven. Four cases are among German nationals.
Experts believe all the patients caught the infection in Germany and brought it back to the UK.
Three of them have developed the potentially deadly complication of haemolytic uraemic syndrome (HUS).
The victims either went to A&E, NHS walk-in centres or had been to their GP.
According to the World Health Organisation (WHO), cases of HUS and enterohemorrhagic E.coli (EHEC) continue to rise in Germany.
Overall, 10 countries have now reported cases to WHO.
Nine patients in Germany have died of HUS and another six of EHEC. One person has also died in Sweden, bringing the total number of deaths to 16, according to the latest figures from WHO.
Many other patients are in hospital, with several needing intensive care, including dialysis.
Overall, more than 1,600 cases of complications linked to the E.coli outbreak have been reported worldwide.
All cases except two are among people who had recently visited northern Germany.
In one case, the person had contact with a visitor from northern Germany.
In England, there have been four new cases overall, including three among Britons.
The other new case is of a German national on holiday in England.
The exact source of the contamination has not yet been determined, according to the HPA and WHO.
The Food Standards Agency has found no evidence so far that produce from possible sources has been distributed in the UK.
The HPA has issued a warning, telling people travelling to Germany to avoid eating raw tomatoes, cucumbers and leafy salad including lettuce, especially in the north of the country.
Anyone returning from Germany with an illness, including bloody diarrhoea, is also urged to seek medical attention.
Victims can require hospital treatment because HUS affects the blood, kidneys and, in severe cases, the central nervous system.
Dr Dilys Morgan, head of the gastrointestinal, emerging and zoonotic infections department at the HPA, said: "The HPA continues to actively monitor the situation very carefully and we are working with the authorities in Germany and with our counterparts across Europe as to the cause of the outbreak.
"We have alerted health professionals to the situation and advised them to urgently investigate and report suspected cases with a travel history to Germany."