Vehicles first used on 1 April 1985 or later
The front windscreen must let at least 75% of light through and the front side windows must let at least 70% of light through.
https
://www.gov.uk/tinted-vehicle-window-rules
Kindly check facts before posting as it's not totally against the law as you stated.
The glass fitted in the ZS EV is seen by some people to be totally NON tinted.
However clear glass by it pure nature of manufacture is NOT totally clear and therefore fully transparent.
Tinting the front screen may therefore not totally against the law, that is true.
But when adding any grade of film to the glass is very likely to push it past the permitted limit.
Any decent tinting company with be able to measure the transparency of your glass first.
I personal know of no tinting company that would consider / recommend a front windscreen tint of any level.
At night time the darkness of the tint is much stronger and in poor weather conditions your visibility is even more greatly reduced.
I only advise friendly caution, what you decide is your choice and your choice only !.
Car insurance companies can be very windy on this subject.
I have just taken this from the Q&A pages of a local tinting company who has been offering training and tinting services for over 20 years.
And he writes :-
CAN YOU TINT ALL THE WINDOWS?
By Law we can't tint the windscreen, and we will not tint anything darker than 70% on the front windows. If anyone has any difficulties or questions, don't hesitate to get in touch with us. The current regulations can be viewed at VOSA.