Investigation of notifiable infectious diseases.
Tracing of contacts.
Exclusion of food handlers from work and children from school.
Offering advice and any necessary follow-up procedures.

There are a number of diseases, which must be notified to the Environmental Agency when diagnosed by a doctor for example:

Some of these diseases, for example food poisonings, may require investigation by the Environmental Health Office. The patient is contacted and interviewed to establish the origin of the infection and to limit its spread. It may be necessary, especially in the case of food handlers to exclude them from work until certified to be no longer infectious so as to diminish the risk of a food borne disease being transmitted to others. For similar reasons, children too young to be conscious of personal hygiene may be excluded from school/nursery whilst they are infectious.

The Agency is kept up to date of the progress of diseases around the world by the UK LINKS Health Protection Agency and the World Health Organization and advice is given to travelers to "exotic" locations who may be recommended or required to be vaccinated against certain diseases.