The problem with a lot of the British motor industry was the quality, because of poor management and labour relations.
The Montego was basically good, but overgeared for caravan towing. I saw the Perkins Prima Diesel engine into production. The validation and reliability testing was the same as used for the Agricultural, Industrial and Construction engines, for heavy duty work. They withstood deliberate abuse very well, I never managed to break one!. We had cars brought to the factory, still going strong after 300, 000 miles of taxi work. The same engine from a Fork Lift Truck was still within new manufacturing tolerances after 7,000 hours, (And FLT operators are not particularly careful of their machines. You should see how they treat the trucks in the Brickyards!)
Sadly, the Engineering skills that made Britain great are diminishing, (Preservationists and Model Engineers are trying to keep them alive), but it is easier to work at getting R S I than to make anything.
Don't knock the few British engineers that are left, be proud of them! . If you fly, in an air liner, it is more than likely that you travelled courtesy of Rolls Royce, and the results of their innovations and skills! Their research produced sealants such as Wellseal and Hylomar; and now they grow turbine blades from single crystals!
They solved problems that beset the first B R railcars, ( I saw it from fairly close quarters!)
The largest yield tightening machine in the world, at the time, (32 spindles) and probably even now, was adopted by a British company. (Ford and Rover were using single spindle versions, but this one was awesome). It would put W range fasteners, 32 of them, into yield, with a 9 ton load, from finger tight . within seven seconds It ended gasket failures, and paid for itself in a year
It is just so sad that so many British managers failed to adopt of the systems proposed by of Deeming and his like, whilst the Japanese did.
Howard