CAN'T FIND REVERSING LIGHT SWITCH FOR VAUX ASTRA J REG?

I HAVE DONE ALL THE USUAL CHECKS TO SEE WHY MY REVERSING LIGHTS DON'T COME ON. BUT HAVE COME TO THE CONCLUSION THAT IT MUST BE THE SWITCH. BUT I CAN'T FIND IT. I KNOW IT'S AROUND THE GEARBOX SOMEWHERE, BUT NOT SURE WHETHER THAT MEANS GETTING UNDERNEATH OR LOOKING FOR IT NEAR THE GEARSTICK.

CAN YOU HELP PLEASE