Hi Dave. Welcome to Just Answer.
How many wires do you have at the location of the switch?
What colors are the wires?
Are you able to post a photo?
Thank you. And your location?
Thank you. How do you currently have the switch wired?
Here in the USA, the green wire is ground, which I believe is referred to as "earth" in the UK.
Can you confirm that the green is used for that purpose there... for grounding? I suspect it is.
Yes green earth
Thank you for the additional information. It sounds like you need one more wire from the switch to the motor, to get it to run in reverse.
Without photos, it may be difficult to help much. Unless, you can post part numbers for the switch and the motor.