mine had the same problem, fixed it last week. Definateley the brake light switch.
They only cost about £6.
It an easy job to do. First of all the brake light switch ISNT the one in the middle. Thats the clutch switch. ( supposed to make changing gear smoother).
Well I never noticed any difference as I took the replacement swicth back to the dealer with the middle one I had taken out, and told them they must have given me the wrong part as the connectors are different) That the clutch switch Sir, dont worry even our own mechanics remove the wrong one sometimes.
The brake light switch is the one on the far left.
Disconnect the electrical connector and and make a mental note of its angle. You'll know what I mean when you see it.
Rotate it anticlockwise and it will pull out.It should need about 45 degrees before it comes free.
Ensure that the plunger on the new switch is pulled fully out. They should come like this as standard.
Insert the new switch in place about the same position as it came out and push in home so that the plunger depresses against the part of the brake pedal.when fully inplace rotate the switch 45 degrees back the the same position you noted before you removed the faulty one. Reconnect the connector and give it a try.
Seems very easy, and it is but one top tip, which caught me out.
When it did mine the brake lights stayed on permanently, even when the ignition was off and the car locked. I ****** around with this for ages. The solution
Rotate the switch clockwise a further degrees or two. This last bit is the part where switch comes out of its locked position when new.
After cracking this the job should only take you ten minutes, excluding removing the lower panel under the steering column and refitting.
Just incase, remove the cover above the steering column, pulls towards you and back.
Two M8 bolts hidden under there.
two M8 bolts underneath the lower cover, one each side
and lastly remove the fuse cover to the right of the dash and the last bolt is hidden under there.
Good luck. its a very easy job and it WILL fix your problem
Simon