“...the man who collected it told me that if the break is not too near the shoulder they’ll let it rest and heal.” Hhhm. I don't know about East London, but in my neck of the woods the RSPCA are hopeless with wildlife casualties, mostly due to woeful lack of funds. My gf is a wild-bird rehabilitator; the local vets refer casualties to her. When they phone the RSPCA about a wild casualty, they are told to euthanise the animal, never mind the species or its condition. Perhaps there's an RSPCA veterinary hospital near you which is able to take and treat such casualties, I don't know. If you find another injured bird, maybe you could try phoning your local vets and asking if there's a rehabber nearby that they'd recommend.