I doubt there is actually a reg for this. Seats in 2 door cars, the tilt MUST work, a fault in the lock mech preventing it will earn you a fail.
Not true, sorry. Theres no fail for the tilt mechanism, it does not need to work for access to the rear seats.
All thats tested is the fore-aft adjustment and the secure mounting of the seat to the car and security of the backrest. On a Mini, the entire seat tips for access to the rear, its hinged at the front. As the seatbelt mounts to the car, not the seat, the belt will hold both the occupant and seat in place. Perfectly safe and MOT worthy.
I've HAD a 2 door Fiesta fail on the tilt lock not working! Not THAT recently I admit, but within the time of computerised MOTs. I also removed the Carledo's back seat on advice from my tame tester for the same reason, i'd fitted fixed front seats. Not that you could get into the back without a big struggle anyway! But no back seat fitted, no tilt required.
I'd thought when I got the MGF seats that they would tilt and allow the back seat to be refitted, turns out they don't tilt, except in the sense you can slide them forward and wind the recliner forward well past vertical with the knob on the side. Not much good in an emergency exit situation! Which I gather is the thinking behind the tilt needing to work!