I can't make out the model from the photo, but there are a few RCDs which look like that. The operating handle is pivoted in the top corner, the "on" position as pictured and "off" has the handle rotate down by anything from 45 to 90 degrees. The black square at the lower right is almost certainly the test button. I can't think of anything else that unit could/would be.
The ELCB is still a violation because they arn't recognised anymore
They've not been recognized for new installs for 30+ years, that's true, but if the system complied with the current edition of IEE Regs. at the time it was installed, can we really call it a violation?
I agree entirely with your basic premise though. I've never liked the voltage-ELCB arrangement anyway. Given the way that the earthing/bonding has clearly been modified in more recent times, there may well be so many parallel paths around that the ELCB has been severely de-sensitized. It's a pity we can't see more detail of where all those earth cables run.
By the way, for non-Brits you can see the way that a basic installation with the voltage-operated ELCB was wired in diagram #4 here:
https://www.electrical-contractor.net/ubb/Forum15/HTML/000044.html
