Downloaded and burned off an ISO and managed to get into the recovery menu.
Automatic recovery? About as much use as a castor on a crutch
No matter I can access the command prompt and fix it that way.
Disk volumes are healthy
Bootrec /fixmbr successful
Bootrec /fixboot access denied
Apparently the only way to get around this is to download another earlier windows 10 ISO and use that instead
Thank God for unlimited downloads, by the end of this one I'm looking at somewhere between 15 and 20Gb of Windows ISO and other related crap over the last day and a bit.