Photo: Martin Pope

“Master switch on, three fuel pump switches out, both mag switches out, ignition key on. Come on, Peter, do keep up...”

Max Girardo, RM Auctions’ European managing director, flaps a giant diagram of the Bentley’s dashboard in the general direction of his general manager, who is swarming all over the car flicking, clicking, switching and pumping.

“Now, ignition panel switch to position one, hand throttle closed, ignition master to bottom position, pump the Ki-Gass three times...”

This is getting ridiculous. How long can it take to start an engine? And what kind of car actually needs three fuel pumps and a Spitfire Ki-gass thingy that whooshes neat petrol into the inlet manifold with all the subtlety of a garden sprayer?

This one does and I can’t quite get the slightly horrified expression off my face as I watch the two men go through the five-minute starting procedure. Australian Jumbo Goddard’s 1924 three-litre Bentley with twin-turbocharged eight-litre engine was once the world’s fastest Bentley, and you’ve really got to want to start it up. It isn’t something that happens by accident, or on a whim. You don’t nudge a key and hey presto. You need to consult a manual and a diagram and follow a series of complicated instructions

“And press THE STARTER!” Max skips in glee as Peter thumbs the Bakelite button and with an audible ring, the solenoid fires the open pinion into the open ring gear.

Funga, funga, funga! BOP, Bop! The old Bentley starts.

Like, er, wow. We all stand around looking slightly embarrassed. Then they turn and look at me.

“Weed,” I squeak. I start again, several octaves lower. “We’d better do a full run-through so I know what I should be doing before I, er, drive it.”

Peter and Max look at each other.

“You have driven it, haven’t you?” I ask. I look from one to the other. The concrete trembles slightly as the old Bentley does its pawing-the-ground thing.

Both shake their heads.

Oh no…

Let’s get one or two facts up front here. First, at least 550bhp. Second, £680,000. Third, 170mph. Fourth, a centre throttle. And fifth, £680,000. This big beast is one of the stars of RM Auctions’ Battersea sale next Wednesday (October 29) and I think they want it back in one piece, preferably without a Ford Escort jammed between the front dumb-irons.

“It’s a phenomenal piece of kit and unbelievably fast, but at really high speeds the front sort of takes off,” Bentley dealer and expert Stanley Mann had warned me. “It’s going to kill someone one day. Even when Jumbo Goddard had it, his wife told him, ‘If you drive that thing again, I’m going to divorce you.’”

Mann looked after the Australian’s car for a short while and prepared it for sale to Wednesday’s vendor, an Austrian who, reputedly, hasn’t driven it very much. I sympathise.

“The engineering is immaculate,” said Mann. “It’s got all the right bits, dials, switches and everything.”

One of the first-ever turbocharged petrol cars, Goddard’s beast is fitted with two enormous Garrett blowers mounted below the twin three-branch cast manifolds. Bentley’s eight-litre six-cylinder engine is a rare thing. Just 100 were built before Rolls-Royce acquired the company in 1931 and, although it is notoriously inefficient, its design and refinement were sufficient to tempt an envious Rolls-Royce to bury the project.

Goddard found his example just after the Second World War in a scrapped ambulance; it cost him £100. He already owned an earlier and much lighter 1924 Bentley three-litre from almost new. He had run through a tuning manual’s worth of performance options, including more carburettors and a supercharger, but then decided to fit the eight-litre powerplant. The work was entrusted to Rolls-Royce and Bentley specialist LG McKenzie, who rebuilt the engine and fitted it to the three-litre’s frame, which had been boxed in with another three-litre chassis to increase its stiffness. The car’s specification also included eight-litre axles, with telescopic dampers and hydraulic brakes. Panelcraft created sporting two-seater coachwork, with British Racing Green leather bucket seats to match the body and wheels. Goddard speed-tested the car at Antwerp in 1962, setting a flying kilometre speed of 222kph (138mph).

This was clearly not enough, and Goddard befriended Wilton Parker, then vice-president of the Garrett Corporation, maker of diesel engine turbochargers. Petrol turbocharging was in its infancy, with the first production example, the Oldsmobile Jetfire, launched in 1962. Goddard’s Bentley provided a stiff technological challenge for Garrett and for Don McKenzie, LG’s son, who had taken over the project.

The result produced 550bhp at 4,000rpm and, with the boost pressure preset at 12 psi, 200bhp (at the wheels) at just 2,000rpm. Before he died, Walter Owen Bentley, the marque’s founder, saw the car in its turbocharged state and is reported to have said to Goddard: “You know, this is just the course of development that would have taken place if only we had stayed in business.”

Goddard returned to Belgium in 1972 and, after overcoming difficulties with transmission lubricants, set a fastest time of 158.2mph. Most people who know the car reckon it is good for 170mph, although whether that would be on the ground or in the air no one really knows. Goddard enjoyed his monstrous machine well into his old age, doing sprints and the Brighton Speed Trials. He died in 1983 and the car remained with his widow until the late 1990s, whereupon it passed through several hands, including a spell at the Donington Park museum.

Now, as the seconds creep by, the temperatures are slowly climbing on the clocks. How difficult to drive can it be?

Very difficult indeed, it turns out, after I confidently vault into the driver’s seat and look down at the dashboard. There are no fewer than 13 separate dials, mostly on the dash but with some out of sight, and 18 or so visible switches. Where to begin?

“Ho! Good luck then!” says Max, scampering off to the safety of his office with indecent haste as I manoeuvre what must surely be a couple of tons of motor car around a car park the size of a guinea-pig hutch.

Graunch, rattle, grate, crash… the gearbox takes some learning and it’s easy to forget to replace the reverse detent, with potentially crippling results on the move. The clutch, though, proves light and, once rolling, so does the steering. That centre throttle is a nightmare, but the action is beautifully engineered, with 13 bell cranks and a similar number of tiny cross shafts taking the movement from the pedal and distributing it evenly between the individual two-inch SU carburettors mounted at either end of the engine.

GRAUF! Grauf. The old Bentley makes me look almost competent as it rumbles out of the car park and into Southend’s busy traffic. With my legs straight out ahead and the steering wheel in my chest, it’s an acquired style of driving and not totally unpleasant, though my heart leaps when I hand-signal left and the open tyre grabs my coat sleeve like an angry crocodile and tries to drag me out of the seat and into the wire spokes. Meanwhile, engine heat pours back though the firewall and the big steering wheel twitches and twists with each tiny surface change.

“Right brake, right brake,” I mutter under my breath. Even so I almost collect a couple of tiny hatchbacks, the first when it completely disappears behind the Bentley’s imposing radiator grille, the other when I leap on to the throttle instead of the brake. With this much power, you don’t make that mistake twice.

In fact the beast is surprising docile at low speeds; the ride is good, the steering light and direct, the visibility is superb. I have no idea what most of the dashboard is telling me, but when I smell a hot engine I pull a button marked “Fans” and see the ammeter register a slight drain, so that’s OK.

Finally the road clears, I open the throttle and the Bentley gathers speed like an approaching storm. You can’t really compare this acceleration with mere cars. There’s a latent energy that just doesn’t exist elsewhere in the automotive world, but no sense of stress, just a deepening exhaust note as the driveline takes the strain like a tug-of-war team pressing their hobnailed boots into the turf. Then at 2,000rpm in second gear the rear tyre swishes into wheelspin with a ring of smoke standing just off the tread an inch from my elbow. Gadzooks! The rest of the car appears to be driving just as normal. Weird. Try it again and whizzzzzz, the same thing happens: the tyre just spins up.

In third gear the L-section Dunlop racing rubber slips and then grips and the Bentley pours on speed like some meteoric mastodon. It feels bigger and heavier the faster you go, and I have to admit to being slightly horrified at the power and speed and feeling as though I were only partly in control of this gargantuan machine. On tiny Essex roads the Bentley needs very careful handling and huge concentration, but it’s also quite the funniest thing to drive…

Who will buy it?

While Jumbo’s Bentley is a unique testament to one man’s fascination with the marque, it remains something of a charging elephant to drive and a white elephant to own. It’s a great Bentley Drivers’ Club car, but with those turbos it’s not particularly welcome to compete against other Bentleys. The engineering is wonderful, but it needs a skilled engineer to keep it fighting fit and that’s not cheap. RM Auctions staff whisper names such as Jay Leno, the American talk-show host, who already owns a tank-engined special and a naturally aspirated Bentley 3/8.

You’d certainly need Leno’s appreciation of engineering to enjoy this car fully and Leno’s deep pockets to afford the bounteous fuel consumption.

Either way, it’s Lot 253 in the sale on Wednesday, and with the estimate almost three times the value of my house, Mrs English has taken my chequebook away. If you can afford it, and if you can start it, you’ll probably want to own it.