No not talking to ground; at 16.06:53 Papa India contacted LHR tower on 118.2MHz and clearance to line up and take off from 28R was given; at this time Papa India informed the tower that they had a small problem.
It may have been the illumination of the amber stick pusher 'low pressure' warning light as it was later discovered that the locking wire of the three-way valve of the stick pusher system was missing.
It was in fact only about a 30 second delay; as Key then advised he was ready for take off and clearance given again.