The 1968 XJ6 blazed a new trail for Jaguar – but which of its first four generations make the most affordable classic today? Is now the time to buy – or should you bide your time?

JAGUAR XJ6 SERIES I (1968-1973) £9990 to £18995
A distillation of four previous models – the MkI, MkII, S-Type and MkX/420/420G – the XJ6 Series I embodied everything Jaguar had learned about post war road cars.

It was a class sensation; few rivals could match its combination of luxury and performance for the money. With 2.8 and 4.2-litre iterations of its now iconic XK straight six available, the Series I’s swansong came in the form of the 5.3-litre Walter Hassan-designed V12.

Prices for good XJ6 Series Is are climbing fast. According to online asking price collator The Market. Having surveyed the prices of 309 surviving cars between September 2014 and February 2018, values are climbing at a rate of 27 per cent a month.

A visit to Car and Classic seemed to bear this out; while prices on The Market peaked at £18,000, we found a range of XJ6 Series Is for sale, from a £9990 1970 2.8 imported from South Africa to an £18995 1972 4.2 car produced in the last year of production before the Series II took over.

JAGUAR XJ6 SERIES II (1973-1979) £5900 to £20,000
Stymied by poor build quality and strike action, the XJ6 Series II nevertheless brought welcome improvements to the XJ6 range; a longer wheelbase (from 1974), another six-cylinder engine choice in the form of the 3.4-litre XK, and the beautiful-but-premature XJ-Coupe from 1975.

Often forgotten by collectors, asking prices of Series IIs are rising, albeit not as quickly as its predecessor – The Market, based on data from 462 cars sold between September 2014 and February 2018, quotes a 14.9 per cent montly growth rate.

While the very best Series IIs (and XJ-Cs) will cost you more than an equivalent Series I, cheaper Series IIs remain available. As little as £5900 gets you behind the wheel of a Condition 3 Series II, rising to £20,000 for a concours example.

JAGUAR XJ6 SERIES III (1979-1987, 1979-1992 for XJ12) £1100 to £15995
The Series III saw the XJ6 in for the long haul. Despite looking dated by the early Eighties, a nip and tuck from Pininfarina kept its lines relevant – by 1981, the XJ-S’s high efficiency cylinder heads had migrated to the XJ12.

Tweaks like trip computers and ‘pepper pot’ alloys meant the Series III maintained its dignity while its troublesome replacement, the ‘XJ40’ continued to gobble up time and dwindling development funds; by 1987 it was all over, apart from the XJ12, which soldiered on until 1992, when its XJ40-based successor, the 6.0-litre XJ81, adopted the nameplate to take the fight back to BMW and Mercedes-Benz.

Scruffy project Series IIIs are still cheap – but trips out will be fraught with breakages. The Market’s figures suggest as little as £1100 will get you a set of keys, rising to £15995 for a show winning car.

JAGUAR XJ6 ‘XJ40’ (1986-1994) £1100 to £15000
While the Series I to III could trace their roots back as far as 1968, the 1986 ‘XJ40’ dispensed with that lineage. For once, a new British car really was so, from the ground up; scaleable AJ6 engines replaced the venerable XK units, while ‘unclockable’ Lucas instrument packs and digital displays set technological precedents.

Sold alongside the outgoing Series III XJ6s for a year, the domestic praise heaped praise on the XJ40, despite having its fair share of teething problems once out on the road. Quality improved markedly by the end of the Eighties, leading to a police motorway car endorsement.

Data from The Market reveals a broad pricing spectrum for surviving XJ40s. By end of production, the range was vast, even discounting the 6.0-litre V12 XJ81 which took over from the Series III XJ12 in 1992. Special variants like the Majestic, Insignia and XJR will fetch more money than even the best XJ6 or Sovereign; as a point of entry into classic Jaguar ownership, you may well score a roadworthy car for less than £1000.

The Market’s figures, based on 493 XJ40s sold between September 2014 and February 2018 lays out XJ40 price boundaries between £1100 and £15,000. XJ40s may well be affordable now – but chances are they won’t stay cheap forever. Once buyers are priced out of borderline project Series Is, IIs and IIIs (and the worst XJ40s are picked clean for parts and then scrapped), prices for even the roughest 2.9 will rise to suit.