Requests for help in the form of a letter or e-mail from a company (real or imaginary) can be used to engage children in a topic.
A letter or e-mail is also an effective way to ask children to communicate what they have found out from an investigation. If it is possible to arrange, children will be more motivated writing to a real person at a real company.
Remind children of the formal features of this style of writing e.g. for a letter to have address and date, for an e-mail to have a subject. Suggest that children list the points they want to make and organise them into a logical sequence before they start. For children who need further support you could compile this list of points with them.