Thanks Ian P.
Sounds more like it.
The motor was getting somewhat hot, but even switching the belt to different pulley grooves to get the motor fan speed up, but spindle speed not, didn't help much as the second switch off proved.
Next time will have to sort out a method of forced draught into the VFD enclosure.
The drilling was when I made a holder for my 5C collets using a step drill & 3mm ally sheet.
Geoff – Heating via electric oil heaters and electric blanket, the latter utter bliss.