To my Knowledge, Most Clearance are given by Data Link now right?
Still got a Clearance DEL but some or most Clearances are done by data link right? Same at EGKK as well?
Only if flight is on time and with certain airlines who report PDC ( Pre Departure Clearance ) recieved, the rest are either on a Revert To Voice as the clearance failed to be acknowledged on time or aren't signed up to the system.
The Clearance Delivery is still a busy frequency at both Gatwick and Heathrow.