Overboost is a mode the ECU goes into when it reads more than 10psi of boost. The engine will cut out and not accelerate until you have lifted off the throttle and re applied.

You are either running a 195 bhp chip which still has an overboost facility but higher up the boost range. I think this limits the boost to about 14 psi...

Or you are running an unlimited boost chip which has no overboost facility.

I noticed you are in Blackpool....I would suggest going to see Stu + Kenny @ Motorsport Developments. They will sort you out.