Presumably this is using the phones in-built GPS, and asking it where it is?. And of course the FCC has nothing to do with the UK, or anywhere other than the USA.
The point I'm trying to make is that it's a capability required in the equipment so something manufacturers must create and include, and it has been in use to some level for a very long time.
UK law may take a while to catch up, but it has also been required here for some years. Any in use elsewhere in the world is obviously "feasible", so also required here.
Part of the OFCOM conditions of service for mobile operators:
4.2 The Communications Provider shall, to the extent technically feasible,
make accurate and reliable Caller Location Information available for all
calls to the emergency call numbers “112” and “999”, at no charge to
the Emergency Organisations handling those calls, at the time the call
is answered by those organisations.
Remember that the GSM system inherently needs to calculate the path length to each device, so the time division multiplex replies can be properly interleaved and not overlap other timeslots.
The GSM system only uses increments of around 550 metres on air, but there is no reason the actual timing system cannot be far more precise and give path length down to a few metres. It still needs two or more towers to get a location better than a radius, though.
Re. the accuracy of locating mobile phones in film and TV, where they have to keep a call active for minutes, to pin down a location - the great lie is that any government agency would not usually have the precise location instantly!