2007 Focus CL Tail/Brake light issue help please?

[Maggotchops]

Hi, hoping to get some help with the tail/brake light issue on my 2007 Focus CL please.

Day time driving all brake lights work as they should (including the top centre brake light) All indicator lights work fine.

Night time driving the tail lights work fine however when the brake is pressed the top rear centre brake light engages, however the left & right tail lights completely go out and the brake lights do not engage? (there is no rear lights apart from top centre brake light)

I have checked all the globes & the light housing connections seem fine, fuses are all fine. I also checked the rear number plate fuse and lights as I had heard it may be linked by means of grounding the brake lights but they fine also?

How can they work during the day but not when the head lights are operational?

Any ideas help would be appreciated