Mike,
July and August are full of festivals, they tend to follow the same weeks year on year, I.E. the first weekend in July or the second weekend in August etc. If you look up froots on the Google search engine it will lead you too their web-site which carries a month by month breakdown of most of the festivals in the UK and beyond. There are two major festivals in August, both week-long ones, one being Sidmouth on the south coast the other being Whitby on the North East Coast, many Catters go to Whitby which is a festival of English, Irish, Scots and Welsh music