Its almost autumn, so the only fertiliser you can use now is an Autumn lawn feed,a granular preparation - breaks down slowly over 6 months.

Thank you very much for this. Since I got your reply I’ve been trying to find an autumn lawn feed which doesn’t kill the moss as well but I’ve not managed to find any.. please could you or anyone else suggest one?

So far as I am aware, all the lawn foods suitable for use in autumn come with mosskiller - its because we usually have damp winters without much sunlight, never mind strong sun, so moss growth is virtually a given during winter in the UK.