OutsideCAS... People in "ivory towers" have no real say in the matter. They are following international guidelines about Controlled Airspace, as are many other countries. What goes on outside CAS in the UK is up to the aircraft operators. However, volcanic ash clouds are not well-known for remaining inside CAS!
As for popping some old engines on an aeroplane and flying into the ash to check the results.... I think that's bordering on insanity. How about if the engines powering the "test-bed" became clogged and it crashed? So you're willing to risk life and limb for this venture?