Nope, clearly is a S65 V8 from the M3 with 470 hp. Clearly it makes zero sense if it was an s85 detuned to 470 and topgear never gets things that wrong where they would mistake the engine completely. He even comments numerous times in the episode that the V8 is quiet and clearly if it were a v10 the exhaust note would be clear as day.
Back to the topic of how they got it. There is no debate on what the engine was!