You're lucky for theme parks because you have the UK's most famous and biggest (and most expensive) theme park, Alton Towers nearby! Bear in mind it's the school summer holidays so it will be packed with kids, but the good thing is you might also spot some money off voucher scheme things running or even get a group booking. If I see any then I'll save them or point them out! I have to add, I've never been there because I'm too tight fisted to pay
I'd avoid London at all costs unless there are any masochists in the group - we're in the middle of planning for the O'lympick period at work and have been told to cut workplace attendance down to a maximum of 40%. Our London colleagues have been asked to work from home, from elsewhere in the UK or to take leave. This is if you can get anywhere around the capital - tube and rail stations will be closed.
Folks on fb know about my weather forecasts (my sad weather obsession, you might say) and I think it's going to be a traditional British summer. Some sun, maybe some hot days, but also some rain and cloud and murk. It looks as though the north of the UK will be warmer than average, the south not so much so, but with a general trend in August for warmer, drier weather.