you can't take photos on the a380 tour, they don't want photos taken in the assembly building.
apart from that you're allowed to take as many photos as you want during the other heritage and panoramic tours. as you're not allowed out of the coach on the panoramic tour you have to take photos from inside it whilst it's going around the site, but you can get decent shots. runway side it's not that great on any tour, but when you're waiting in departures at the airport you can take excellent landing and takeoff shots and can also see the testing going on on the far side of the field, it's clearly visible.
we planned it so that we did all 3 english tours in one day, with an easyJet flight out of gatwick first thing, and returning in the evening.