Wow! thanks for the pictures DukeDesmo....Looks like any bits would find their way to the sump plug without too much trouble.
I pictured the hole being directly above the gears.
Looks like a filter strap is the way forward..I have just tried mine on without turning it, and I think it's going to work.
The flats are a 51mm Octagon. So something like an immersion heater (Sadly@86mm) box spanner would be ideal....But as far as I can tell no such thing has been invented yet.
When the new one arrives I will get down to business with it...If it won't shift then I guess Dirty will be a happy chap....