Brake and Tail Light issue Clio 2004

Hi Everyone,



I was told that you guys are the best people to ask regarding an issue with my Girlfriends Clio.



I was following her back to our home the other day and noticed that her offside tail light wasn't working. Her brake lights however, were fine.



So I purchased a new bulb (Offset pin, double filament) and went ahead and swapped it over.



This is where I'm stuck.



Once I had changed the bulb, the tail light is working, but the brake light has stopped working.



So to clarify, existing problem was tail light not working, brake light fine. After new bulb installed, tail light working, brake light NOT working.



So I wondered if anyone had any ideas as to what to test/try next? I haven't checked the fuses yet, nor have I checked/replaced, brake light switch.



Any advice appreciated.



Thanks in advance, Aaron.