For long lens work I use a Jobu gimbal head they aren't cheap but they are very well made and work beautifully.
http://www.tripods-heads-gimbals.com...al_heads?id=13 this is the one I've been using for the past few years, I'd highly recommend it. The alternative would be a heavy duty video head (like the Manfrotto 501), they can be very solid, but the movement is not as quick and easy as a gimbal. Either option would be good for long lens work but not so good for other photography, so it's worth working out where your priorities are before buying. Not sure where you are in Norfolk, but I'm near Swaffham if you want to meet up and try the Jobu.