[Laird Scooby]

I'd say make use of the front fog switch and fit a pair of front fog lamps Alan.

I would suggest wiring it correctly though, use a 4-pin relay with two integral diodes, one flywheel diode and one blocking diode and take the feed from the dipped beam wire via the fog lamp switch to terminal 86 on the relay and terminal 85 to the main beam wire.

Connect terminal 30 via a fuse to batery +ve and termianl 87 to the fog lamps.

Having a quick look online, it appears that relays with two integral diodes are NLA, you'd have to get a 4-pin relay with an integral flywheel diode and add a blocking diode between the switch and terminal 86 so regardless of switch position, the relay coil would only be energised with dipped beam, the full beam filaments would act as an earth path for the relay coil.
When full beam is selected (and by extension, dipped beam deselected) the blocking diode would be reverse-biased and therefore not conduct, relay coil is de-energised and fog lamps extinguish.