Citroën started thinking about adding a luxury car to its range in the mid-1960s, perhaps with one eye on the market left vacant by the collapse of Facel Vega in 1964. Facels had been powered by enormous Chrysler V8s, but French tax law now made anything larger than a ‘15CV’ (equivalent to about 2.8-litres) virtually unsaleable. So Citroën enlisted help from Maserati to design and build a relatively small, but high-performance, V6 engine. A technical agreement with the Modena firm was signed in 1968.

Maserati came up with an all-alloy 2.7-litre V6. It’s often referred to as three-quarters of a Maserati V8, though according to Citroën specialist and SM owner Stuart Agar, if there is a relationship it’s a tenuous one as few parts are interchangeable between the two engines.

Source of the rumour is the SM V6’s 90 degree angle between the cylinder banks, unusual for a V6 but normal for a V8. It seems likely that the wider angle was used to reduce the height of the engine, in turn helping to keep the bonnet line low.

Striking looks and efficient aerodynamics were both parts of Citroën’s plan. The SM’s steel monocoque body was wide and low, with a teardrop taper in plan view that meant the rear track had to be nearly 6in narrower than the front. Underneath there was a development of Citroën’s hydropneumatic suspension system, familiar from the DS, with interconnection between front and rear on each side and automatic self-levelling. At the back the wheels were suspended from DS-style trailing arms, but the front wheels were mounted on unequal length transverse arms. Where the trailing arms forced the wheels to roll to the same angle as the body, compromising grip, the new transverse links kept the SM’s front wheels vertical as the body rolled to minimise understeer and maximise traction.

As with the DS, the powered hydraulic system was used not just to maintain the car’s ride height, but also to level the headlights (and steer the inner lamps into corners), to power the brakes and to provide effortless steering. With just two turns between locks the steering was very direct, but the combination of power assistance and zero steering offset made it so ‘irreversible’ in its response that Citroën said even a burst front tyre would not cause the wheel to fight in the driver’s hands. To give the driver more confidence at speed, artificial ‘feel’ was engineered into the system.

The SM managed to blend high levels of grip with an excellent ride, though in usual Citroën style the car assumed large roll angles in fast corners. Road surface irregularities did little to worry the SM, and at high speed the car’s sophisticated aerodynamics made it stable and secure. It was a fine open-road cruiser.

But not the easiest car to get used to. Stuart Agar took a while to get used to his SM. “It was left-hand drive and I found it really difficult to place it on the road,” he says, “and the sheer everything-you-know-is-wrong-ness of it – you had to unlearn everything you knew about cars and start again. The steering, the brakes, the suspension – the rhythm of the car was nothing like what I’d experienced before.”

It took a high-speed cross-country journey for Stuart and the SM to click, and now the Citroën spends most of its time in that role. “I use the car for what was intended,” says Stuart. “I tend to do long journeys in it. I use it for taking me to modern art galleries in France.”

Stuart’s SM was one of the first fuel injected cars, sold new in Spain in 1972. It came to Britain sometime around 1980 with around 17,000km on the clock. It sat under a posh London apartment until, supposedly, both car and flat were lost in a game of cards. The proud new owner then started up the SM – and it burst into flames.

It was bought as a wreck and restored around 1985 – at a time when, says Stuart, parts for the SM were still available new. It was used daily for a year, then went into relative retirement. Stuart then bought it from Andrew Brodie Engineering, having never before driven an SM.

Stuart has named it Tamara, as a plaque under the bonnet confirms, after 1930s artist Tamara de Lempicka. “She painted these particularly futuristic, very overly stylized portraits of people you could imagine driving an SM,” he says. “They tended to be minor European aristocrats, whose lives were really decadent, and didn’t have much of a future.”

Stuart seems unlikely to part with, erm, her. “You get to the stage with a car where you’ve invested so much time and effort that you can’t just replace it with something else,” he says. “I feel like the car owns me.”

Nothing can prepare you for driving the SM. The long door opens onto an inviting cabin with multi-adjustable leather-clad hammock seats and chrome-plated fittings. The single-spoke steering wheel is typical Citroën, and ahead of it sit an oval speedo and tacho, together with a group of warning lights in a matching oval cluster.

The chrome gearlever has a precise action, the clutch quite a heavy one. Noise is subdued at low speeds, but as the revs rise the Maserati engine makes it presence felt – the V6 snarl a little at odds with the SM’s calmness. The steering is, well, curious: no kickback, no real feel, finger-light when manoeuvring but quite hefty at speed. The strong brakes are operated by a rubber button on the floor which responds to pressure rather than movement. It’s all very alien, but put aside your prejudices and you realise that the SM goes rather well. Performance is strong, the ride excellent and well-damped, and the whole car gives off a sense of imperturbability. Get in tune with it and it’s very, very impressive.

Buying a Citroën SM

The SM holds traps for the unwary – particularly if the car is being brought out of storage. “There are so many things that can catch you out, and the consequences are disastrous. If it’s been sitting for 10 years, when you start it up the valves will drop off and smash the engine to bits,” says Stuart Agar disarmingly. “You’ve got to take the heads off and fit solid valves, but that alone is £1500 before you start looking at other bits and pieces.”

The original fuel injectors also caused engine fires, though by now many cars have had later, non-incendiary injectors fitted. Andrew Brodie Engineering has developed a variety of improvements for the cars, including solid exhaust valves, an uprated alternator, a more progressive throttle linkage and an uprated air conditioning system with a quieter, more modern pump.

The SM requires regular maintenance befitting its high-performance character: “It’s got twin overhead camshafts on each bank,” explains Stuart. “They’re chain driven, and the chains are tensioned manually. Every 12,000 miles you have to take the cam covers off and tension them.” Even though the job takes only a couple of hours, some owners consider that to be an unreasonable additional task and skip it, with inevitable results.

» Andrew Brodie Engineering