Brake light problem

This evening I changed the faulty nearside brake light bulb but it isn't working. The bulb is fine because the tail light element works and if I put it in the offside cluster, both tail and brake elements work. It's just the brake element not working when it's in the nearside cluster. The cable connector to the cluster seems to be fine and also the high level brake light is working.

Any suggestions welcome before Mr Plod pulls me over! Thank you.

Catman