I'v always assumed that was the case, in exactly the same way I assumed that 999 operators were able to use OS grid references. Never tested that theory...
I can't speak for the (former) British Telecom emergency operators, but the former British Rail - now Network Rail - Telecoms network switchboard operators directory system could be searched by OS grid reference - either 10 or 12 digit from memory - as well as by station name, bridge number, overhead electrification gantry number, (quarter) milepost and track-side plug-point number (A box about every 100m with sockets to plug a basic phone in for track-side workers before the days of mobile phones). I'm not sure if it ever included Lat & Long, as this was pre-GPS.
The information returned by the search included a 12 digit OS grid reference for the location, postal address (where appropriate), authorised access route from public roads (for track-side locations), Electrical Control Room in electrified areas (to turn the juice off, if not already done!) and the direct phone numbers for the emergency switchboard for the relevant local police, fire and ambulance services for that exact location, as well as Coastguard and Mountain Rescue if appropriate.
From that, I would *
assume* that the emergency services at least are geared up for location information by OS grid reference, even if BT don't have a clue what to do with it, but that is only an assumption and is based on what was happening on the railway 20 years ago, when I was responsible for the staff entering this information for what used to be the Eastern Region of British Rail. This information was worked out manually from OS maps and BR track diagrams, a **
very** time consuming activity, although it did have the advantage that I had access to 1:50,000 and 1:25,000 OS maps of the eastern half of the UK north of London. Not that I ever borrowed them for cycle tours and Audaxes, ooh no never!! Ahem!!