Any advice please on how to go about replacing the halfshafts on my 36 Ruby Mk2 ?

Commiserations; I know how you must feel having had the same happen to me.
The problem is that the half-shafts are fitted from inside the differential cage and this has to be split to remove and replace the half-shafts.
Personally, I think while you are doing it you may as well go the whole hog and rebuild the whole back axle with new bearings if in any doubt and new seals, either felt or rubber, along with gaskets etc.
I didn't mess about with second hand halfshafts but went for new ones from John Barlow as I live quite near him.
The really tricky part is checking and adjusting the pinion and crownwheel mesh.
I took all the casing parts down to a local vehicle cleaners and had them steam cleaned.
Cleanliness is really important if the axle is to run for many years without any more attention.
I wish you luck and hope that you are mobile again before long

Colin,
If it's of any help, I've got a set of digital photos with some notes describing the job. I've replaced a half-shaft on my own RP saloon some years ago and since then, I've done one on a 1934 Nippy when I took the photos. I'm afraid the notes aren't very comprehensive, (I now write blow by blow accounts of every big job I tackle), but the photos might help you understand how it all fits together. The diff is really much simpler than you might think. If you'd like the notes and photos, let me know where to send them and I'll bang them onto a CD for you.

Tom

Okay, it's an extra expense I know, but I'd suggest you invest in a copy of Doug Woodrow's Book "The Austin Seven Manual" (publisher Mercury Vintage Services), which explains how to correctly pull apart and reassemble everthing on every model. That way you won't make any expensive mistakes, knowing the correct sequence and what goes where and how. You'll later find the book invaluable for the rest of your car's maintenance/repair when needed, plus if you're like most of us you'll finally succumb to having an extra Seven or so (it's a disease worse than Bird Flu), then you'll use the book for the other models as well. Good Luck, Bill in Oz.

Back on the road !
Job completed at weekend, 2 new shafts fitted. Now to get the brakes bedded in again and pulling up straight. Thanks guys (esp Tom) for your help and advice.
Colin