UK Car Repair: reversing lights, gear shift linkage, wire colour

Question
I have a astra estate and can not get the reversing lights to work.
The bulbs are fine and sometimes if i slam it in reverse the lights work.
I have looked for a switch under the gear stick and under the car and even on the gear box but cant see anything please help

Answer
There is definitely a switch and it will be adjustable.  It is most likely somewhere on the gear shift linkage, you just have to look harder.  You can look at the wire colour going to the bulbs and find that colour wire somewhere on the linkage or box.