BMW’s M division has built a special lightweight one-off version of the E60 M5 as part of the 25th anniversary celebrations for the iconic four door saloon.

Revealed this morning at BMW’s prototype workshop at the Nurburgring in Germany, the celebratory M5 is described by M division’s head of development, Albert Biermann, as “the M5 CSL we never built”.

Among the changes brought to the new car is a heavily modified version of the standard M5’s 5.0-litre V10 engine. The highly strung, 90-degree unit has been enlarged with a longer stroke taking its capacity up to 5.5-litres, making it the largest engine to ever feature in an official M-car.

Also included as part of the engine overhaul is a carbonfibre manifold boasting a increased capacity air box and a secondary oil cooler – the latter requiring modifications to the front bumper, which gains an additional air duct in the place usually dedicated to the license plate.

Official power and torque figures have not been released but Biermann hints the output peaks at “around 580bhp and close to 400lb ft”. That’s up from 407bhp and 348lb ft with the standard M5.

Channelling the added reserves back to the rear wheels is a beefed up version of the M3’s seven-speed double clutch gearbox. The Getrag engineered unit, operated via steering wheel mounted paddles or push/pull gear lever, supplants the standard M5’s sequential seven speed manual unit, offering smoother and more rapid gear shifts.

Further changes centre around the body, which receives a carbonfibre roof as part of a weight saving program that has pared a claimed 50kg from the standard M5’s 1830kg kerb weight.

BMW’s M division has also stripped down the interior, doing away with the standard front seats in favour of two carbon fibre backed pews, while the rear seat has been ditched altogether.

In terms of its suspension the new M5 remains close to the standard specification. “We’ve altered the mapping of the variable dampers but the geometry remains the same,” says Biermann.

No performance claims have been made for the powered-up-and-pared-down M5, but Biermann says it is “comfortably faster the standard M5’s 4.5 sec 0-100km/h”.

He also confirmed to Autocar that the new one-off M5 it has already lapped the Nurburgring in the hands of long-time BMW race driver, Claudia Huertgen, in under eight minutes, making it some 20sec faster around the legendary German circuit than the standard M5.

“It’s a lot gutsier than the standard M5,” says Huertgen, who this year drove the new Alpina M6 GT3 race car in the FIA sportscar championship. “You can sense the added drive out of corners. There’s more bottom end shove. I’m pulling over 180mph under the bridge at the Doettinger Hohe [the fastest point of the track]."

Yet despite the investment that has gone into creating the new uber-M5, Biermann says it is destined to remain a one-off.

“Right now we’re concentrating on the next-generation M5. This car has been fun to develop but there are no plans for production,” he says.

“around 580bhp and close to 400lb ft”.

BMW has finally confirmed that it developed an M5 convertible 20 years ago, but canned it a week before it was due to be launched due to sales concerns.

The long-rumoured car was shown to a select group of journalists at an event celebrating 25 years of the BMW M5, and autocar.co.uk has obtained exclusive photos.

BMW confirmed that the car, which had two lengthened front doors and seating for four, had been developed for sale at a price of £50,000.

It was all set to be launched at that year's Geneva motor show, with BMW booking space for it on its stand, but a week before the event it was canned.

BMW confirmed that it was abruptly dropped as it believed it would result in demand for non-M 5 Series convertibles, which could have harmed sales of teh highly-profitable drop-top 3 Series.

Will have Active Aerodynamics, which blanks off parts of the grille and cooling intakes during warm-up and under light throttle load

It’s official, the all-new 5-Series is here! A consistent class-leader since it was introduced back in 1972, the sixth-generation of the ‘5’ promises to be every bit as revolutionary as its forbearers. Auto Express was at an exclusive unveiling of the car in Munich to bring you these first official images and all the details that matter.

With this car it’s clear that BMW has put the Chris Bangle days behind it. The controversial ex chief designer brought his unique brand of love it or loathe it styling to the last 5-Series, but BMW has kept things more conventional this time around. Gone is the awkward boot lip, replaced instead by cleaner lines and tidy proportions, with only two main creases running along the side of the car.

In the flesh the low bonnet and shark-like nose give it a sportier and more elegant look than the formal styling of the outgoing model. In fact it appears more like a bigger brother for the 3-series than a down-sized version of the 7-Series we all expected. Something which Adrian van Hooydonk , design chief for the BMW Group claims is a coincidence: “It looks closer to the 3-Series because we’ve taken a sportier direction with the design. In turn, the design for the new 3-Series will have to be even sportier,” he revealed.

A wheelbase of 2,968 millimetres, the longest in its class, translates to an additional 13 millimetres of leg room in the rear – just one highlight in a much improved cabin. The trademark angled centre console – puts the focus firmly on the driver, while an optional glass sunroof floods the cabin with light. The major design cues, such as the widescreen display and black-panel technology, which appears to be a piece of interior trim when the air-con is not in use and lights up magically when you turn it on, are lifted from the 5-Series GT. But whereas the GT focuses on light and space, the 5-Series is a cosier cockpit-style affair, hinting at its dynamic capabilities.

The engine line up includes four petrol and three diesels. Stop-start is included as standard on the 520d, predicted to be the biggest seller in the UK, while a new eight-speed auto transmission with wheel-mounted paddles can be ordered as an option over the six-speed manual, or comes as standard on the range-topping 550i.

With CO2 emissions of 132g/km and 56.5mpg the four-cylinder 520d is the most frugal 5-Series ever. It’s joined in the diesel line up by two six-cylinder units – the 525d and 530d. Both 3.0-litre single turbo engines, they produce 201bhp and 242bhp respectively with the more powerful of the two still returning a creditable 44.8mpg.

Three straight-six petrol engines are offered – the 523i, 528i and 535i, all of which feature direct fuel injection. The two former are naturally aspirated, while the 535i is turbocharged resulting in 302bhp and a 0-60mph sprint in just 6.0 seconds. But if even more power is a priority, the range-topping 550i, featuring the 4.4-litre twin-turbo V8 from the 7-Series, offers just that. Despite packing 401bhp and peak torque figure of 600Nm, the 550i is capable of 27.2mpg.

While the styling might have been toned down, BMW hasn’t dulled its focus on the 5-Series being a car for keen drivers. New double-wishbone suspension at the front is said to strike the best balance yet between handling and comfort, while the Drive Dynamic Control system allows drivers to modulate throttle, steering and gearbox setting via four modes – Comfort, Normal, Sport and Sport+. The chassis is 50 per cent stiffer than the old model as well, for an overall weight penalty of only 15 kg.

For the UK market, standard equipment will be more generous than ever. All models now come with leather upholstery, automatic air conditioning and Bluetooth connection as standard. Among the myriad options, customers can specify a park assist system, collision warning with auto brake and 360 degree surround cameras which give a bird’s eye view of the car on your display, for negotiating especially tight gaps and spaces.

Despite the additional standard kit, the 520d’s price tag has only risen by £735 over the model it replaces. Further up the diesel range the 525d and 530d start from £32,380 and £36,300 respectively. The petrol line up begins at £30,560 for the 523i, climbing to £36,290 and £49,440 for the 535i and 550i respectively. The newcomer hits showrooms on March 10 minus the 520d, which follows in June.