The UK is far too small and irrelevant to mandate anything of that magnitude industry-wide, but they need to act as if they are still important to placate the Brexiteers.
People seem to be assuming that this means we're going to be inventing a Great British Charger that is gratuitously different from USB-C (I think the plug would have to be exactly 2/8" wide by 2mm thick to properly reflect UK measurement practices

) - of course that would be ludicrous.
But think a bit beyond the knee-jerk reaction. The universal charger idea isn't
just aimed at what socket the top 3 premium smartphone brands put in their devices (and for whom it made sense to switch to USB-C
anyway) nor is it just aimed a phones any more.
The UK is still a significant market, and there
are plenty of products - made in the UK or overseas - specifically designed or adapted for the UK market, which currently
aren't affected by the EU directive.
That's not to mention products made for the
other vast areas of the world that don't follow EU rules and could dump their non-USB-C stuff on the UK market.
Prime example: the Great British Mains Plug (popular topic of internet debate) is already established. That means that every big tech manufacturers
already has to make a special power brick (or at least a specific slot-in plug head) for the UK market. The UK could certainly influence the design of power adapters (E.g. I'm not sure that the EU directive forbids adapters with captive USB-C cables - which would probably have been more important than regulating the device end!) Maybe we should stop cheap, bare minimum USB-C adapters being bundled with phones to nudge people to get with the program and buy one charger for all their devices (debate)?
Keyboards with British English key layouts (not the same as International English) are manufactured/adapted specifically for the UK - do we want to leave a loophole that let QWZREZ inc. flood Amazon UK with wireless keyboards, or even cheap laptops, with cheaper barrel plugs?
Also, even Apple regionalise the
OS and packaging for UK Macs - so a UK "difference" could, for example, be requiring a particular form of "Charger not included - Requires any USB-C certified Charger supporting 100W or higher" notice on the packaging. Otherwise, sellers will do their level best to convince you that only their premium-priced own brand charger will work. I wouldn't entirely put it past the less scrupulous "large tech companies" to (say) add a nag screen to the OS if you use an off-brand charger while the location is set to "UK" - the EU won't care.
Then there's this:
The big problem in the UK is all the transport infrastructure with USB A at the seats.
Forcing the bus operators and train rolling stock operators to upgrade everything is key to making this happen.
I don't think this is affected by the EU directive, which focusses on rechargeable devices. Certainly wouldn't require existing vehicles to be modified (you can charge perfectly well via a USB-A to C cable). Should it? These trains and busses are already extensively customised for the UK market so it would be perfectly feasible to have our own rule or exemption.