I am sure you know this but Single Engine Turbo prop are perectly allowed to fly in UK airspace. Also they are allowed to fly under a Public Transport AOC but VFR only....
The real change will come when/if Public Transport Single Engine IFR is permitted for JAA reg A/C, in the UK.
As much as I would like to see it happening, I have heard about the "next year" thing since 1997 (Got directly involved not before a couple of years later)!!! It will happen and there is no reason why it shoulnd't but the talk of a Caravan dealer are to be taken with pinch of salt.
Again, I am not saying it won't happen but there are few issues such as whether or not the CAA will require two crew, cost of installing a TAWS (Turbine certified with more than 9 seats), Landing and take off minima, *ETOPS type of rule in the event of an engine failure.
*term used loosely but I remember talks about requirements regarding gliding distances and approved suitable landing surfaces (determined by the Operator).
Anyway, if it happens, my Rating is still current so....