
Because it has a number of features that mean it cannot pass the safety inspection to be allowed on U.K. roads.
First the big one, it cannot pass the safety inspection for pedestrian safety should it collide with someone, the design geometry and materials the Cybertruck are made from mean that it’s impossible for it ever to do so. The stainless still is too rigid, the angles and height of its front end too wrong.
Similarly it’s not going to pass the tests for collisions with other vehicles and the safety for their passengers. The construction method doesn’t have the necessary crumple zones built in.
There are no side indicator lights a U.K. requirement.
The rear lighting strip is the same colour, which doesn’t conform to U.K. road rules about having rear indicator lights in a orange colour within a certain light frequency range.
The front continuous light strip similarly is against U.K. law.
This basically means a Cybertruck cannot ever get a Certificate of Conformity to allow it to be driven on U.K. roads.
Is “banned” the right word? It doesn’t meet UK vehicle specifications. The vehicle doesn’t meet UK rules on weight, its sharp edges are not permitted for pedestrian safety reasons and its exterior lighting is inadequate.
Nobody in the UK took a look at the Cybertruck and said “hey, let’s ban that”. The rules were in place before the Cybertruck was even glint in Elon Musk’s eye.
For an example the other way, check this out. This is a forthcoming release by the small-volume manufacturer Morgan, which specialises in producing cars with retro styling (but modern internals).

It will not be for sale in the USA. Why? Because it doesn’t comply with US rules. This was already known and US sales were never part of the business plan. Would you say the US “banned” it?
Edit: lots of people are asking what US rules that Morgan doesn’t comply with. Sorry, I don’t know. The above information came from an interview with Morgan’s CEO who simply said that the car won’t be for sale in the US because it doesn’t comply with US regulation.
I’ll give you three of the many reasons.
the sharp corners. British design rule require curves of a minimum 3.2mm to reduce harm to pedestrians should the vehicle collide with one. And those sharp edges cannot be changed – they are engineered to be part of the structural strength of the vehicle.
It does not have crush zones as required by most cars. So in a crash it transfers much more energy into the passenger cell resulting in much more severe injuries to the occupants.
It’s too heavy to drive on a normal car license in the UK. You need a lorry licence to drive it.
Oh, and I’ll give you a forth reason. It’s 2.4 meters wide, almost the width of an articulated lorry (semi truck). Most of Britain’s two lane roads have lanes of just 3 meters width, meaning that there is only a 30cm clearance each side of the vehicle as it sits in the middle of the lane.
Try getting two of those vehicles past each other on the road from Keswick through Borrowdale and up to the Honister slate mine and you’ll see what I mean.