The sparkies ended up wrapping the fuselage with linked mains extension leads and plugging in a couple of 2kw electric heaters for a few hours in an attempt at degaussing. It didn't work and I can't recall what happened next.
The current was limited due to the heaters, and rightly so. If you can do it again, connect the coils to a high powered AC welder at a couple hundred Amperes, slowly reducing the current after turn-on.