The production XJ-S coupes received the HE V12 engine in 1981, which also helped to stem their downward-spiralling sales figures. Nonetheless, they were still barely scraping fuel consumption of 15.7-28.3 mpg, which is why the new six-cylinder 'Advanced Jaguar' AJ6 engine did not arrive a moment too soon, finally replacing the old XK unit. The 3.6-litre version was the first six cylinder Jaguar engine to have an aluminum block and cylinder head, and it enabled Jaguar to start fitting complex electronic control systems and reduce emissions. It was fitted in the XJ-S from 1983 right up until 1991. But the biggest boost to XJ-S sales came with the launch of the cabriolet version, the XJ-SC, in 1983. Not quite a full open-top - the structure was not rigid enough to do away with the roof bracing - it had removable roof panels and a rear canvas hood, made and fitted by the Aston Martin Tickford workshops in Bedworth. The production process was slow, but sales picked up again, and by 1985, it was thought worth putting the HE V12 in the cabriolet as well. The sales of the XJ-S and XJ-SC models helped Jaguar through the early '80s, when its saloon range desperately needed a huge overhaul.

The Series III XJs are now well on their way to classic car status, and although it's still possible to find some very cheap ones (less than £1000 could buy you a runner), the gulf is widening between the price of the bad ones, and the best. Buy the very best you can afford, watch out for botched 'restorations', especially of XJ-S and XJ-SC models, and avoid privately-sold cars with missing history. Their maintenance will have been skimped on. Best to pay more and buy a warranted car from an independent Jaguar specialist. XJ12 models are particularly cheap, as few people want to take on something so thirsty these days.