There are 2 warning lights on the instruments relating to VSA ESP.

1 light is a yellow "VSA"
The other light is directly below the VSA & is also yellow & is a warning triangle with a "!" symbol inside the triangle.

If there is a genuine VSA fault, both VSA & triangle symbols illuminate together when vehicle is running.

The fault I am getting is that ONLY the triangle warning symbol stays illuminated when vehicle is running. The VSA light goes out.

This triangle symbol should only stay illuminated when you press the "VSA" button on the dash to tell you that you have disabled the VSA. When you press the VSA button again the warning triangle symbol should go out reactivating the VSA.

Scan tool reading show that the ABS ECM recognizes that the VSA button is being pressed.
There are no fault codes in the ABS system.

Has anyone got any pointers???

Have you checked the other controllers, vsa can be disabled if there are faults in other controllers that are linked, eg engine ecu?

Have you lost throttle control too? I've come across this when somebody took fuses out of the fusebox to inspect for a blown one, then put them back in the wrong location!
If I remember correctly it was the under-bonnet fusebox (customer was looking for a blown headlamp fuse - which turned out to be a dead bulb).