Thanks John R decided to go with 220v AC as 12v dc did not work.
Removed board from the lathe, and tested the contacts, that should be normally open, they were CLOSED, which would account for not being able to switch the lathe off normally, measured the resistance across the coil it was 14.4 K ohms.
Decided to remove the relay from the board, it was quite difficult due to the heat sink on the back being in the way, it is as big as the board, I could not remove the heat sink because there are 7 components stuck to it with adhesive pads, and soldered to the board.
Once the relay was off the board I put 220v through the coil and the contacts closed, and opened, every time, (sods law) but I still intend to replace it.
Thanks John S the PDF is very useful, I did a search for that but could not find it.
The only place I could find a replacement is in China so I have some ordered. I have everything crossed now hoping that the relay IS the only problem.
Will let you know how I get on.
Thanks again to both John's for your help.
John