Ariel has marked the 25th anniversary of its Atom spaceframe sports car with the new 4RR - the most powerful version yet. 

With its uprated Honda four-pot sending a huge 525bhp and 406lb ft to the rear axle, the new special edition is far more powerful than even the outrageous, 475bhp Atom V8 from 2011.

Ariel has not quoted any performance figures, but the standard Atom 4R, on which the 4RR is based, has 400bhp and claims a 0-62mph time of just 2.7 seconds.

Expected to roughly match that car's 680kg kerb weight (to give a stunning power-to-weight ratio of 770bhp per tonne), the 4RR could trim that sprint time below the 2.5-second mark, making it one of the quickest-accelerating combustion cars yet to come out of Britain. 

Just 25 examples of the "circuit-focused" special edition will be produced to order, and full technical details will be announced later this year.

Ariel says it has been engineered to enable "the most serious track drivers to explore the limits of the lightweight Atom, while utilising the full extent of their driving skills".

Though heavily evolved over the last 25 years and four generations, today's Atom is familiar in its styling and construction from the original.

The first-generation Atom, which pioneered the company's trademark tubular space-frame chassis, used a 120bhp Rover K-Series engine, while the Mk2 switched to the Honda Type R engine that's still used today - with a supercharger added as an option in 2005 to bump power to 275bhp.

Maximum power was ramped to 300bhp with the Atom 3, which introduced a new chassis, suspension system and bodywork - as well as the bewinged Atom V8. 

Today's fourth-generation car, which provides the basis for the R and RR, is all-new apart from the fuel filler cap, steering wheel and pedals. It made the switch to turbocharging as standard, and produces 320bhp even in entry form.