Brake lights failed on 1.4S

[Si_GTi]

A colleague at work has a Polo 6n2 1.4, and her rear cluster's brake lights are no longer working on both sides. The high-level LED brake light does still work though, so I assumed the bulbs had failed on both sides.

I've had the bulb holders out from both tail-light clusters and the bulbs appear to be in good condition with no damage to the filaments, so here's the question:

Short of changing the bulbs is there anything else to look for that might cause the brake lights to have stopped working? I thought of the brake pedal sensor located above the pedal in the driver's side footwell but assume that if the sensor failed, the high-level 3rd brake light wouldn't work either

Will change the bulbs tomorrow and see how things go, your help will be appreciated