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Brakelight indicator comes on while driving

Why does my brakelight indicator come on while I’m driving? Brakes have been checked. Brake fluid level indicator replaced. Adequate brake fluid. So why does that brake light indicator come on?

in england on most cars,the same light comes on when u set the handbrake(parking brake)it has a switch that activates when u pull the lever,maybe this is faulty??or needs adjusting?

Is it possible that the light you see is supposed to indicate a bulb failure? If so, check to make sure someone has not switched bulb sockets around in the tail lights, and check that the wattage is exactly the same in all the bulbs in the brake circuit. Mismatched bulbs can set off a warning light.

The other possibility is more disturbing. Could the light be a brake system failure warning? That would mean an imbalance in pressure between the two brake circuits. If it was not inadvertantly triggered by recent brake work, it could indicate a leak at a wheel or a failing master cylinder.