The power output of Mercedes-AMG upcoming A45 appears to have been revealed accidentally by a German insurance website.

HUK24, an online insurance provider, has stored powertrain specs in a drop-down list for the new range-topping A-Class, examples of which were registered for road use in Germany in December.

UPDATE: The 415bhp Mercedes-AMG A45 S has been officially revealed - read the full story here

The details, although unconfirmed officially, reveal that there will be two different power outputs from the car's 2.0-litre turbocharged petrol engine. The 'base' model will produce 387PS (382bhp), while the flagship S variant makes 421PS (415bhp). Both will put their power down through all four-wheels, and are set to go on sale later this year.

The output of the standard model is already in excess of the 370bhp produced by the outgoing A45, with the top-spec car a full 45bhp more powerful. That should translate to 0-62mph of around four-seconds, and possibly less.

The video, which the German firm has called 'Not another Christmas video', showed an A45 in a bold multi-coloured disguise livery lapping a test track in Germany, and showed the car performing a series of powerslides.

While few official details of the range-topping A-Class have been revealed, Autocar has previously learned that it is set to have the highest specific output for a production engine in the world, eclipsing even the McLaren Senna's 789bhp V8.

AMG boss Tobias Moers told Autocar earlier this year that the A45 will get "well over 400bhp" from its new engine, which is expected to be an extensively re-engineered version of the current car's 2.0-litre unit.

That means it will have more than 200bhp per litre, ranking the car at least 12bhp-per-litre higher than the current A45 and beating the current specific output champion, the 197bhp-per-litre Senna.

The model, dubbed by AMG insiders as 'The Predator' as a nod to its extreme performance, is expected to serve a rival to Audi Sport's RS3 in the pairing's ongoing super-hatch fight, while also ensuring the A45 offers stronger straight-line performance than the forthcoming BMW M2 CSL.