The official line is NO.
However, most people are not really bothered by it - it isn't really a highly sensitve/secret area is it ?.
I take mine in from time to time, and only been asked once why I had it - I just said it was for company use and they were fine (it wasn't of course).
On days like the final day of Concorde, AF1 and the A380 coming in, almost everyone airside had a camera/cam corder of some sort and neither the BAA or Police were bothered and now with mobile phones even more people have them !!.
If it is just a pocket sized point and shoot type camera, then you shouldn't have too much trouble as long as you are discrete with it and where you use it and what you shoot.
Quite a few of the BAA marshellers even have their big SLR camera's with them airside in their vans, so they don't usually mind as they understand the obsession/hobby.
Occasionally you may encounter a jobsworth who will pull you up (probably more likely in a regional airport as they think they are more important), in that case apologise, say you were not aware of the rules as there are no signs and it isn't explained anywhere and they will normally be ok if you are apologetic and don't get arsey with them. The worst they can do is confiscate your camera, but you would get that back later anyway.
Happy snapping.
