Driving around to loosen the spring as suggested previously is not an option if like me you discover a broken bottom leaf - mercifully still held together by that all important clip. The only way to shift the spring on my 4 Seat Tourer was to buy a long length of 1 inch bar, remove the number plate and get a mate to drive it out from the front with a big sledge, whilst I held the bar. I made sure it was long enough to be well clear of any missed swing of the hammer!
It took some mighty blows before it shifted leaf by leaf each with a sheared off piece of rivet inside! Thankfully no damage was caused to the chassis rails. The really good new was being able to locate a spring with an exactly matching set amongst the many held in the BA7C spares shed. The broken top leaf on this spring was replaced with one from the old spring, and a new rivet made and fitted.
The bar is available for hire at three shillings per hour.
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

Ah what you should have under your seat is a pair of rear spring U bolt plates together with 2 lengths of 3/8" stud bar and 4 3/8" nuts which make a useful get you home clamp if you should break a rear spring leaf.

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