When I think about 'unfortunate' English cars, I'm thinking primarily about postwar English cars. (There was a very, very good article about this in the old Automobile Quarterly magazine, the one featuring the greatest English car of all, the Hirondel.) I have tremendous respect for the Rolls-Royce Ghost and Phantom II, particularly the American ones made in Springfield that 'got no respect'. I'm surprised you didn't mention the Squire, one of the best-styled cars ever made.
As you probably know, the Citroen SM was originally designed to take the 4.7/4.9L engine from the Maserati AM115, which was first reduced in displacement and then cut to 6 cylinders to fit it in a better French tax class. (This is obvious when you look in the engine bay and see the distance between the engine and radiator, and the peculiar fan extension). It's a logical thing to put the better engine, with a better 5-speed transmission, "back" in the SM, and this fixes most of the compromises and weirdness with the car as built. There is little effective change in the weight distribution, and of course the characteristics of the suspension ensure there is little change in the road handling. It most definitely runs better with the four-Weber V8; perhaps entirely too well.
I confess to being a great fan of real varnished wood and Connolly leather, which is why I liked John's Cars in Dallas so well. It came as something of a surprise to me that the curb weight of something like an XJ6 actually considerably decreased with the substitution of something like an LT1 and its appropriate transmission for the original Heynes six, even as the mileage went up (considerably, with the GM-spec ratio in the final drive) and the usable top speed went up even more. Fixes for all the squirrelly little compromise rubber pieces, shocks, and bushings, too.
I assume you mean something like a Riley Nine Kestrel
not the little Sixties box...
Meanwhile, there is something from Australia that I think gives the Squire a run for the money: