First place I would check is the gearbox switch, think it's located to the front left of the box.
Remove the plug and get a short length of wire and bridge across the two plug terminals with the ignition on, if you get reverse lights then you will need to replace your faulty switch, probably source new from local motor factors for around a tenner, unless Finn has some sitting around.
Shouldn't be a fuse cause you would have no indicators.
Hope this helps lads.