As QDM says, Kemble will be busy - let's not forget the British Grand Prix weekend at Silverstone. Not sure how many helis will going in on Sunday but it's bound to be around 150 with many more flights than that from all the feeder sights around there. Be a good place to steer clear of.
Picking up what ChilliM says, there can be quite high concentrations of gliders on competition weekends which are quite popular at this time of year. While the Notams I think usually declare the comps. there isn't an easy way of communicating the tasks which are always set immediately before the comp starts, to the general GA fraternity who are likely to be passing and it can lead to 20 or 30 gliders all in the same general area.
My thoughts and sympathies are with the families of those who died today.
2Sticks