Nene Valley Rock Festival will be held at Grimsthorpe Castle, near Bourne, Lincolnshire, in September, with FM and Focus two of the headliners. “We limit our tickets to 1,000 a day,” says director Tony Castle. “We’ve all seen pictures of Glastonbury where most of the crowd might as well have stayed at home and watched it on TV because they are only watching it on a big screen. Limiting our tickets is a bit of a risk because of finances, but we w…