aye because its in your contract it is legal, if it is not on your contract then it is not, i would give it a look over but if they are doing it i would think that it is in your contract as your employer wouldnt want to be sued over something like that
In the same way you can legally film in a public place (with a few restrictions) if it's their property they can also. Covered by the same rules of the CCTV cameras in every shop, town centre, park, public toilet etc. etc.