This sounds interesting but at the risk of being a killjoy i'd be a bit cautious about this, it could be a ruse to suck more money out of people under the guise of the "environmentally friendly"/"now available in the UK" routine.
4-stroke dirt bikes undoubtedly have come on a long way and are impressive but they've also made the sport a lot more expensive for the average guy in the street, and a lot of people are apparently now going back to 2-strokes because they're simpler and cheaper to maintain. On the other hand 4-strokes are able to dominate at the top level because the factory teams are able to afford a complete engine rebuild after every race.
In the '90s Honda built a 400cc 2-stroke for the Dakar Rally called the EXP-2 which was more powerful and cleaner than the equivalent 4-stroke.
Wikipedia:
"With the utilization of a redesigned exhaust port valve and the ARC (Advanced Radical Combustion) system engaged, the engine would produce a pre-ignited combustion effect at low throttle that would completely burn all fuel in the chamber compared to how a conventional two-stroke engine would lose part of the intake charge.
[1] The result decreased two major drawbacks of two stroke technology of both incomplete combustion of fuel at low RPM and expulsion of unburned fuel at high RPM".
Check out this link also:
http://www.motorcycle.com/manufactur...xp2-14293.html
This may be a good thing or it may not, but the fact remains that politics and fashion killed off 2-stroke motorcycles and a lot of people now mourn their departure, check out how much an immaculate Suzuki RG500 or a Honda CR500AF (a made-to-order CR250(alloy)-framed, CR500-engined motocrosser) sells for.