There have been a couple of articles on Twinis in "Classic & Sportscar" magazine, the most recent being on the Deep Sanderson racer.
A couple of years ago the magazine featured a Twini built for a US auto museum.
The consensus of opinion is that a Twini is a ball of fire to drive, but back in the day when BMC, Downton, and John Cooper were playing with the concept certain issues were found with engine synchronisation; problems that almost cost John Cooper his life. It was at that point that the Twini development programme was cancelled. An interesting bit of kit, though.
But the concept of 4x4 Mini wouldn't lie down and die. The tiny Austin ANT off-road vehicle may have been canned after the 1968 formation of British Leyland but the car's 4x4 transmission - this time with a single front, transverse engine - was adapted to a rallycross Mini in the early Seventies.
British manufacturers seemed to be very keen on four-wheel drive back in the Sixties, and it was tractor magnate Harry Ferguson's FF Developments that led the way. There were Ferguson 4x4 protoptypes of the Jaguar XJ6, Triumph Stag, and Austin 1800, which is not to forget the FF Ford Capri. However, it was left to tiny Jensen to blaze a trail with the actual production of a 4x4 road car: the Jensen FF in 1967.
I suppose the likeliest British candidate to mass-produce a 4x4 road car would have been Triumph. It's compact FWD Triumph 1300 of the late Sixties, with its longitudinal engine was later coverted to RWD for the Dolomite of the early Seventies. Could explain more, but this is better:
https://9700vc.blogspot.com/2008/10/4wd-triumph.html