SSH failing (consistently, not intermittent now)

SSH authentication is failing today:

FATAL ERROR: Disconnected: No supported authentication methods available (server sent: publickey)
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

I definitely have access, I switched to HTTPS and everything worked fine (but by default I use SSH on all my repos).

I don't know if this is related to the SSH problems that were occurring on 31 January, but in that case it was intermittent failures, in this case it's all the time.