Obligatory Top Gear link.
The bikers who can drive 3 wheelers must pass their full bike test, it is possible to ride a small bike on a A1 or a p licence and never qualify for larger machines - but you would have to keep doing the CBT at regular interals.
A car driver can drive a 3 wheeler as long as it is car based - no requirement for a crash hat, some 3 wheelers are bike based - must have a crash hat, and some things fall in between.
Bike riders are allowed to drive a ‘light car’ - quad or trike up to 550 kilos, so if the 3 wheeler was above that then they could not drive it - for example you can’t drive a Smart car on a bike licence and yet, crazily enough, you can drive a Caterham(or is it Westifield?) 220, there is one version of the Ariel Atom a biker can drive or even the Westfield XTR2 - there are custom versions of these with around 300 bhp This can only be done on the full B1 licence.
A full night’s sleep, a few hours of work (being unemployed, that is a GOOD thing), and I’m back there. Watching the videos, now. Gee, in Atlanta they let newswomen be, ahem, sturdy? In Chicago they are skeletal.
However, the jokes just make themselves.
“Dundalk Engineering in Ireland, formerly repairers of locomotives, had taken over production of the Kabine from Heinkel - a logical step as half of Heinkel production had already been going to the British Isles.”
Much like it had twenty years before (slapping my thigh with simulated hilarity).
Okay, not good jokes.
I saw the Morgan 3-wheelers at the Goodwood Festival of Speed. They look gorgeous. Very much a throwback to the 1930s. But they’re not everyday cars.
And I can’t fit in them.
The only three-wheelers I’ve ever seen here are Reliant Robins painted up with the “Trotters Independent Traders” logo from Only Fools and Horses. I assume they’re rented for novelty purposes.
I saw a Trotter’s version just the other day in the Lake District. A few years ago at the 24 Hours of Le Mans I saw a gang of them, 3 painted up in Gulf Racing Porsche colours and one as a Silk Cut Jaguar.
There was a “3 wheeler” car designed around a motorcycle back in the early 80’s. The designer’s last name was Bede, an aircraft designer of some fame in the aviation community. The design was called a Litestar and unlike most 3 wheeled cars looked cool as shit. IIRC wheel wise it was basically a motorcycle with training wheels on either side. If you were going slow or turning it would tip a bit and ride on one of the training wheels. Since it could only be on 3 wheels at any given time it was considered a 3 wheeled vehicle by some jurisdictions.
My good link for a website on it appears to be down and I don’t have time right now to do a search so your on your own here.
They got very good gas mileage and looked very cool. I am surprised somebody hasnt redesigned a homebuild kit around a good common and good value for the money motorcycle.
ahhh, heres one:
That’s pretty awesome. Now I’m thinking of painting my Hyundai in 555 Subaru Rally livery. 
We saw this one not too long ago; he was about to set off on a fairly long trip (considering the car and the roads!) to a meet-up of similar cars, iirc.
That is close to being the coolest car I’ve ever seen.