Jaguar stunned the post-war motoring world when it unveiled the drophead XK120 at the 1948 Earls Court Motor Show. With a confirmed top speed of 120mph, the new Jaguar was the world’s fastest production sports car and at its heart sat an all-new, twin-overhead camshaft 3442cc six-cylinder engine that in various guises would go on to power a seemingly never-ending generation of iconic big cats. A coupé version was launched a couple of years after the roadster and the Jaguar XK120 quickly made a name for itself on the international motorsport scene.

In 1954, Jaguar upped the stakes and launched the much-improved XK140. Upgrades included rack-and-pinion steering, better braking, telescopic shock absorbers all round and a more spacious interior. The radically revised XK150 arrived on the scene in 1957 featuring a longer bonnet, a one-piece front screen and disc brakes. Here are some further improvements for all three cars from the 21st century.

In order to squeeze a few extra horses out of any XK engine you can fit an upgraded stainless steel exhaust system, together with a multi-branch manifold. Most Jaguar parts specialists will be able to advise on the best system to fit and David Manners (0121 544 4040) stocks a stainless steel Falcon exhaust for a 3.4-litre XK120 for £442 to give you an idea on prices. When it comes to engine rebuilds and carburettor conversions, much depends on the depth of the owner’s pockets. XK specialist Twyford Moors Classic Cars (02392 570900) is able to rebuild XK engines in house to any state of tune and the cost of a basic overhaul for a standard 3.4-litre unit starts at £10,200.

A five-speed gearbox conversion kit for a XK120 from SNG Barratt costs £3606 or Twyford Moors Classic Cars can undertake this useful upgrade for £4370. Fitting a new radiator to an XK during a rebuild makes a lot of sense, especially if the car is used for long distance touring or on the track. SNG Barratt (01746 765432) can supply an aluminium radiator for £798. Even a freshly overhauled cooling system may need a helping hand in hot weather and a Kenlowe electric fan to keep under-bonnet temperatures in check can be sourced from David Manners for a very reasonable £147.

Like all classic cars, Jaguar XKs can suffer from electrical woes and to help keep them at bay SC Parts Group (01293 847200) offers a high-output starter motor that provides 200 per cent more power and uses 50 per cent lest current on start up for £294.

Upgrading an XK120 or XK140’s front drum brakes to discs transforms the way these cars drive and Coopercraft International can supply a complete kit, including aluminium callipers, for a XK120 with steel wheels for £1589. The XK120’s rear suspension can be beefed up by fitting telescopic dampers and Twyford Moors Classic Cars quotes from £1800 for this conversion, depending on what extra work is required once the car has been stripped down.

Wire wheels are a popular but very expensive option and the price for a single painted wire wheel from SNG Barratt costs £312.16, while a chrome Dayton wheel alternative costs about £50 more. The same company can also supply a front suspension repair kit for £168 (XK140) and a Polybush kit for £281.42. A comprehensive front suspension service kit for an XK120 is available from Guy Broad (01676 541980) for £715.27.

Many specialist trimmers can offer what seems an unlimited choice of interior upgrades for a Jaguar XK, such as non-standard colour leather and carpets, plus a walnut veneer dashboard and door cappings. A popular interior modification is a pair of aluminium- or steel-framed bucket seats. Guy Broad can supply steel-framed tilting bucket seats fully trimmed and ready to install from £1620 each. The same company can also provide a pair of aero screens for a XK120 for £708 while David Manners can add a leather bonnet strap and associated fittings to compete the Le Mans look for £82.80.

Boot lid racks are a popular choice with many XK owners and SNG Barratt offers a chrome example for £535.39 with an optional luggage strap available for an extra £48. Maintaining originality on expensive cars like these XKs is essential and The XK Parts Specialist (024 7647 1217) currently has a good stock of remanufactured front and rear chrome bumpers and overriders for all XK sports cars.