Finally got somewhere today.
Decided to take off the hub nut and use this cheap puller to wind out the drum: l bought the puller three months ago for replacing trailer wheel bearings. But the old worn bearings simply fell off each hub on the trailer. So it got stuffed in a large drawer mentally labelled Another Unnecessary Purchase.
But no! It saved the day.
For some reason l didn't photo brakes etc once drum was removed. Working against the clock for Sunday roast, l guess.
So l cleaned up and greased internal pivots and spring points. Adjusted brakes until locked, then two clicks back. Then on to adjusting handbrake back to appropriate position.
BTW the drum and wheel hub were well and truly mated. So a bit of knocky knocky soon sorted that out!
Draper 1" drive comes to our rescue. Plus additional help from the lovely Debbie Magee, and a five feet long scaffolding pole.
Cheap puller served me well.
And enough time to make a cauliflower cheese, too!
Thanks to all for your suggestions.