UJB 1/the scotish TMA is class E upto FL245 os it is ok for an IMC holder to file IFR...but 2/the airways to the south have a base of FL65 and are class A so it is hard to see how the holder of an IMC could not breach the rules without flying well to the east.
3/i hope the +4c was refering to airframe icing as you are 100% corect about carb ice.
the flight could be made leagaly as long as the exit from the TMA was made aprox 20 miles east of the TLA vor and D510 was not active.