If a Very pistol is held by anyone it is subject to a firearm certifcate, some police forces took the veiw that one person on the staff should hold the certificate and other named staff could use the pistol within the airfield.
This was much in line with the regulations governing shooting clubs where new members could use guns (and be technicly in posesion of a firearm without a certificate) if under the supervision of a named club instructor.
I guess the requirment for each ATCO to hold a firearns certificate is all part of the "security gone mad" times that we live in.