Hi I have found a dead leaf beetle in my loft do I need to act further?

In the absence of more specific information I cannot see that any action is needed. "Leaf beetles" are members of the family Chrysomelidae, but this is a big group (>35000 species). Some leaf beetles are serious plant pests in some areas (e.g. Elm leaf beetles, Colorado beetles) but I doubt they will do much harm in your loft.