Fuse is 15 IIRC but the switch on the gearbox is a common fail.

 

Thanks upspex,
I took the undertray of today and found the switch. Removed the plug and shorted it out, reverse lights and parking sensors worked, plugged it back in and it i some working again. Not sure how long it will last, so going to order up a new switch anyway.
Also while I was there I removed some rust from the subframe and sprayed it, also cleaned out the undertray as it was full of muck where it sits against the subframe. This can't help when it gets wet and propaply is part of the cause of the rusting.
Attached a pic of the switch location looking up from underneath.

 

Replaced the switch today, removed undertray and with a 22 mm ring spanner managed to crack it loose from under the starter motor, then forced the spanner on above the starter motor and got it loose enough to remove by hand. Fitted new one and alll seems ok.
Took about 1/2 hour in total.
Cheers SRR

 

So stripped the old switch, and its burnt out.

Cheers SRR