Failed reversing lamp - 205 - Andrew-T
Having found that the bulb is OK, what is the most likely cause of a non-illuminating rev.lamp on a 205? Is the gearbox switch likely to fail, or is the wiring or fuse box more probable (other items on fuse 1 are OK) ?
Failed reversing lamp - 205 - Baskerville
Most likely the switch on the gearbox. Very cheap and easy fix. You may find that the backlight for the clock has gone, too - it's on the same circuit if I recall, and tends to pop before the fuse.

Chris
Failed reversing lamp - 205 - Ross_D
Also, check the earth points. Is it the newer type cluster with the reversing light in the lower valance or the earlier type with it incorperated in the cluster? (The earth points are slightly different for the two)
You can easily test the reverse switch for continuity with a voltmeter.
Ross
Failed reversing lamp - 205 - Andrew-T
Ross - it's K-reg with separate reversing lamp, but from previous fiddlings I seem to recall it is connected to the left-hand cluster. Another possibility is that the original aftermarket alarm was hacked out recently - they could have knocked something off the fuse box.
Failed reversing lamp - 205 - Andrew Hamilton
Lamp may test OK but contacts on lamp or in bulb holder may need cleaning with metal polish. Finish with WD40 spray to protect. On putting lamp back wiping action clears any excess. Alternative solution if 12V detected on light contacts but light off is to rebend or pack contacts out.
Another possibility is carelessly drilled hole went through cable breaking circuit. Otherwise it is a painstaking approach of checking continuity using a meter.