Just a quick update, cheers to all of you for your advice very much appreciated!!
Well, I've changed his diet to a raw one with veg/rice and after just 2 weeks you can barely see his ribs and his hip bones are also barely visible. I've had no problems making the switch, he has taken to it like a duck to water.
The change in him not only in build but mentality is quite shocking!! He has sooooooooo much more energy, he is running around the fields like a nutter and today I have had success, no not a rabbit, but he did sight and chase (very fast!) a HERON!! It just took off in front of him and