Stop Light

Xantia 1.9TD SLX 1996
The stop light has illuminated twice on the way into work today (Sunday boo hiss). Both times it has gone out immediately so I didn't stop.
I've checked the hydraulic fluid level, the oil level and the water level. All are fine. The engine isn't overheating either.
The only work done recently for the MOT was replacing the front disks and pads and I have had the low pad warning light illuminate briefly a couple of times since then. Presumably the garage didn't plug the pad sensor in properly. I haven't had the opportunity to check yet as it's been dark and freezing since it happened.
Any ideas?

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