Any body tell me why my car could be under-boosting and only boosting at 10 psi its frying my brain any help would be appreciated cheers

I'd give Martin a ring here http://www.subaruservicingyorkshire.co.uk/

 

Top bloke if you haven't spoke to him before and will give you some great advice or off for you to take it up and he will have a look

:) 

could be a number of things - air leaks, fouled actuators. Check for any codes or as Gambit suggests give Martin a shout