OK switches arrived and I took off the switch assembly from the handle.
Continuity check on the original switches showed that they were both OK, strange.
Fitted new switches and found that the machine would not lock ON, removed assembly again and found that the switch I fitted in the ON/OFF position needed to go down further than the other to operate, only a mm difference but enough to prevent it operating with the mechanical limit on the ON/OFF button. swopped them over, reassembled.
Runs, but now unable to turn OFF the brush bar from handle. Take apart again. Investigate the operating system, switch is OK and if the unit is assembled without the brush bar button all works OK. Looked again at the interconnect between the ON/OFF and the brush bar switch and found that the lower end of the brush bar switch had a small lip on it, and the handle cover moulding wasn't square, small amount of filing and all now pass by each other OK. Quick spray with silicon lube. Reassemble again and this time ensure that the tongue on the interconnect slips into the cam in handle and plug in.
Now ON/OFF switch stays On and the brush bar is controllable by the handle switch. Can be turned OFF and ON independent of the main switch. If brush is OFF when main switch turned OFF, it will be switched ON again when mains is switched ON. Now operates as it should.
Worth the £6 I spent