In reply to all: I had two 1.5 kg bags of oranges and the first of them has now been dealt with according to St Delia's Dark Chunky Marmalade recipe.
Stage one of this featured orange wrestling and an explosion of kitchen stickiness before producing a beautifully scented and witheringly bitter liquor. Stage two, completed yesterday, included much boiling foaming orangeness, even more considerable and well-distributed stickyness and some cursing of St Delia.
As a result of these labours I now have a baker's dozen jars of utterly delicious grown-up tawny marmalade. Sweet and bitter with a taste that lingers in the mouth long after it has gone. Marvellous stuff.
Heaven is a piece of toast...
T.