Aeromad,
18 seater (expensive) avgas burning Trilanders compared to 19 seater avtur burning Do228's!
The Do228 had to be UK certified for, in the old days, Suckling Airways to operate it, not sure if the, currently produced, 'NG' variant is considered as being the same beast or not.
If it isn't considered the same beast then I'd hazard a guess there would be a similar problem with the, currently produced, Twotter.