Just submitting this note to anyone else having ssh-key submission problems.
Initial attempt at submitting my public key to the website by cut and paste failed; it seems when I pasted, the space after the string "ssh-rsa" gets deleted by the website edit box. Probably because the HTML edit box optimises the use of what appears to be a useless space character; but this breaks the key!
To rectify I explicitly entered a space character after the "ssh-rsa " and the key was accepted.
The original fault dump I was getting was:
Cloning into 'occt.git'...
Permission denied (publickey).
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.