Good point Dave. Luckily I was at home when I discovered the break and yes, I now carry a clamp made up much as you describe. I mentioned the clip holding up the leaf together; the significance being that the clip prevented the broken bottom leaf from dropping down on to the road where it would have kicked into the tarmac, probably with nasty consequences!
Ron

I thought it best to provide a by the book method Paul, Woodrow recommends removing the hubs because of the risk of damaging the brake drum securing screw thread in the hub.

I used Henry's version, with the added "drive after loosening the bolts" and it was an incredibly easy process, taking an unhurried day to replace both rear springs.
Andy B