Thanks in advance for any assistance/advice, I really appreciate it.
Basically I was advised that my nearside brake light wasn't working yet when I took it to get the bulb replaced (I know, lazy lazy!) everything was fine, all brake lights were functioning. I was then told again that it was out so while Louis was parked on my drive I used a prop to hold the brake pedal down and all brake lights were fine. I then switched the engine on and the nearside brake light isn't working.
I've seen a few suggestions about replacing the switch at the top of the brake pedal, I'm happy to do this if it's the right fix. I'm not convinced though.
If anyone has experienced this as well or has a different suggestion of the cause please let me know.