Officially, all filming and photography within the airport requires a permit. See here
http://www.heathrowai...otography&search=true
and here:
http://www.heathrowai...aphy+FAQs&search=true
However (While I've not used Heathrow for ages) I've seen loads of people at Stansted taking pictures of friends and relatives, without ever being challenged by anyone. The only areas where their are prominent signs forbidding photography are in the zones where security checks are carried out on hold baggage (and, for arriving travellers) at immigration control.
Mobile phones can be used throughout airports (other than at the actual passport control desk for arriving passengers).
Chris