Got my Mondeo booked in for an MoT on Wednesday, anyway was doing the basic checks round it today see if there was anything noticeable that needed doing (e.g. bulbs etc) anyway had it reversed up to my garage door to check brake lights etc and noticed that when I put it into reverse, if I hold the gear lever in gear, the reverse lights are on, but as soon as I let go of the lever, the lights go out? (with reverse still selected and the car obviously able to reverse)

What could be the possible cause of this/is it an easy fix? Ideally wanna do it myself to save cost come MoT time etc..Cars an M reg (MK1) 1.8 TD if that makes any difference

Cheers

John