Cheers Best / Simon,
Plumber has been today and removed 10mm replaced with 15mm. Bled the system which seemed to take a while and i admit he had me a little worried however the rads were getting warm though the study was struggling. He turned all other rads in house off and all 3 new ones were kicking out the heat, he then balanced the system even having some rads in the house <1/4 open!
He told me to leave it a few days to let it settle down but he might have to come back and tweak it a little.
Thanks for all your help it is greatly appreciated. In honour of your help i donated some money to a couple of guys at work doing a charity bike ride to 'spread the good will' if you like.
Thanks again
Paul