and all other UK cars are no longer UK
That's a slight overstatement. Whilst we focus on the niche end of car production, the following companies, inter alia, are still UK-owned and doing quite nicely:
(Bristol - not doing so well...)
Caparo (really very niche)
Not sure old Queeny would want to be driven in any of those, though. Her Majesty's R620 (http://uk.caterhamcars.com/cars/seven-620-r) would certainly make for rapid meet-the-peoples.
The UK also provides much of the engineering expertise and componentry used by the rest of the motor industry. Motor sports throughout the world are similarly dependent on the UK's engineers, even your IndyCars have been known to use UK-produced power plants and gearboxes.