The Ultima looks at home in the paddock at Mallory Park; just another race car booked in for the traditional Wednesday morning test session at the Leicestershire track. The difference is that while everything else has arrived on a trailer and is attended by mechanics, the Ultima drove here. It's fully road legal, with number plates, tax disc and road tyres, details that are easily overlooked, it seems, especially since by the end of the session the GTR has lapped pretty much everything else on the track, even stuff on slicks...

A mechanic wanders up and asks: 'What championship do you race it in?' He's surprised when I tell him that I don't and then asks what it is, perhaps mistaking the 'Ultima GTR' graphics down its sides for sponsors' decals. He's even more surprised to hear it's made a couple of miles away in Hinckley.

Ted Marlow has built a tidy little business around the Ultima, originally created by serial sports car designer Lee Noble, famous of late for the Noble M12 GTO. Ten years after taking it on, Ted sells about 70 GTRs and Can-Ams (convertibles) a year and exports them around the world, almost all as kits. Yet they've been honed to such a degree and are finished to such a high standard that the term 'kit car' seems derogatory. Ted prefers 'self-assembly supercar'.

This car is a factory-built example, a new model specifically for trackdays. You might be wondering why the Ultima needs to be developed for track use, but that's Ted for you. The regular GTR would probably acquit itself very well on track, but Ted wanted to be sure.

Visually, the GTR has changed little since David Vivian drove one to Le Mans over two years ago (evo 17) but what would you change? There is now a front splitter, though, a jutting black ledge that helps balance the aerodynamic effect of the long-established bi-plane carbon rear wing. It's constructed from marine ply rather than carbonfibre so that it doesn't crack or rip if it hits the road, and it was developed in the wind tunnel. It makes the GTR stable at the 200mph it's capable of with the right spec of small-block Chevy V8.

Pirelli has served Ultima well, but an approach from Goodyear led to Ted trying a rather exclusive tyre, the Eagle F1 GS-Fiorano, developed for the Ferrari F50. The rear is the same 335/35 ZR18 the GTR already used, the front slightly wider at 245/35 ZR18. Ted says they give the car a weightier feel but only because the shoulders are squarer, putting more tread on the road and giving more grip. They're very effective in the wet, he says, so rain needn't stop play, they last well, and they're not expensive - ΂£200 each for the fronts, ΂£300 for the rears.

The engine in this car is a mid-range unit - a 350 cu in (5.7 litre) with dry sump lubrication and an Edelbrock carb that produces 425bhp and 440lb ft. It was chosen over bigger capacity V8s for its quicker-revving nature, and here it's hooked up to a Porsche five-speed 'G50' transaxle (a six-speed is offered) with a right-hand gearshift.

Post yourself into the driver's seat and you're surrounded by simple design beautifully executed. As the demo car, it has the works, including Alcantara- trimmed bucket seats and facia, and a Stack instrument pod. Standard fixtures include the substantial roll-cage, the floor-hinged, fully adjustable rose-jointed pedal box, Willans harnesses and a Momo wheel. The door tugs shut with a quality thunk. Hugged by the high-back seat, looking through the bubble screen between the flowing front arches, it feels like a de-luxe GT racer, and you can even have air conditioning.

Press the starter button and the V8 erupts into life and settles to a blustery idle. The right-hand shift is probably the best I've yet tried in an Ultima, with a firm, positive, mechanical action, while the unassisted steering (2.4 turns between lock stops) is seriously weighty when you're manoeuvring.

The steering lightens up once you're rolling but the GTR is no city car - the carb-fed V8 will chunter on a light throttle, inducing a mild kangarooing, so you have to play the weighty clutch and accelerator to smooth things out. The chassis is quite sensitive on heavily crowned roads, too, but neither matters much on track.

Ted recommends adjusting the dampers for circuit work - simply a case of flipping up the front and rear bodywork and turning the collar on the top of each damper clockwise by 15 clicks. As each has a range of 60 clicks, you can effectively alter the handling balance; if I'd had the time I'm sure I would have gone quicker.

As it happened, the GTR was the fastest thing out there anyhow, even though it was understeering a little too strongly for my taste. It feels substantial, encouragingly solid, yet it's not a huge effort to drive very fast. In fact, if it hadn't been for the race cars out at the same time, I'd never have guessed it was lapping so quickly. The steering is light and feelsome, the right-hand shift is co-operative and positive, only the shift into fifth, which takes the lever close to the body, needing strong guidance. The ride is smooth, too, suggesting the damping could be stiffened, making it feel even sharper.

You'd need to add a limited-slip diff if you went that way, though. Out of the hairpin the tail would swing out under power if you stabbed the throttle hard just before the apex, while a more tentative approach would simply spin up the inside rear tyre. Again, like the understeer of the set-up as I tried it, this makes the Ultima friendly for the less confident, who'll be goggle-eyed enough at the phenomenal pace and thunderous soundtrack down the straights.

This actual car would cost ΂£64,000 but pare it back to its trackday essentials and it would be around ΂£46,000. Build it yourself and it could be yours for ΂£40K, seriously tempting when you consider how much performance and quality it delivers, and the very different experience. Plus you get a thrilling trackday car and a roadgoing supercar for the price of an M3.