Unless the UK updates the The Road Vehicles Lighting Regulations 1989 which you can probably guess from the year. has not been updated in a while.
Unfortunately LED bulbs will continue to technically illegal.
I say technically because the 1989 law sites the use of "incandescent bulbs" repeatedly and therefore by omission LEDs cannot be legal under those regulations.
when we were part of the EU, lighting regulations followed the type approval system and so cars that met type approval being manufactured with more modern lighting systems such as HID, LED and laser, were legal under type approval but there was still no law to make conversion to LEDs legal.
There are headlight units around for some cars that have been type approved and can be bought and fitted aftermarket such as Osram Xenarc headlights, but if you go look these up you'll find that they are very Very expensive and only cover a few models of highly popular cars.
There is another company called Vland who also make after market headlights cheaper for a host of different cars, with LED bulbs, however it is not clear if these have undergone type approval for use in the EU and they again have a limited range of models they cover which does not include Fiat but suggests they cater more to the US market (despite being a German company).
I imagine that italy has updated their vesion of our 1989 regulations, for us to do the same and for the government to make LED bulbs legal for use in any car they would have to (potentially) carefully set very specific rules on the construction of the bulbs and undertake some pretty stringent and costly testing to make sure the bulbs were/are compatible with a very broad range of cars.
I can't see Italy having gone to that extent, but in the UK that is potentially what would be needed, so they are very unlikely to do it.
Far easier to just let the manufacturers deal with it using the type approval system and the manufacturer's like it because it ties you in to buying costly genuine replacement bulbs from your nearest parts department.