Vauxhall Antara engine stop /start light

Most common cause is a low car battery voltage , worth load checking and also alternator charging rate

Battery cold 12.5v /engine running charging at 14.8v so don't know

This is from owners manual might / might not help . Could try switching on / off Deactivate the stop-start system manually by pressing the eco button. The deactivation is indicated when the LED in the button extinguishes. Conditions for an Autostop The stop-start system checks if each of the following conditions is fulfilled. ■ The stop-start system is not manually deactivated ■ the bonnet is fully closed ■ the driver's door is closed or the driver's seat belt is fastened ■ the vehicle battery is sufficiently charged and in good condition ■ the engine is warmed up ■ the engine coolant temperature is not too high or low ■ the engine exhaust temperature is not too high, e.g. after driving with high engine load ■ the ambient temperature is not too low ■ the defrosting function is not activated ■ the climate control system does not inhibit an engine stop ■ the brake vacuum is sufficient

Thanks for that i will check all switches and censors are clean and working properly.