Took Fm's advice on this and used two old cards (AA membership and snooker club cards) with araldite.
First of all i cleaned all surfaces to be glued and used sand paper to get a good joining surface. Joined the two parts of the splitter with three bits of card (cut up and rolled to mimick the curve of the inside of the splitter) , on the top, side and bottom on the inside. Gluing one side, waiting to dry/harden and then doing the other piece. Big chunks were missing where the drill holes had been ripped away, these areas were filled with specially cut pieces of card and araldited into place, supported inside with oversized card cut outs.
Waited for everything to dry and then back to blacked the join and all the scuffs on the bottom. You can hardly see the join and all the repair work is invisible once the splitter is in position.
I'll probably go over the join with a light sand paper and then re back to black it, but happy with the result thus far.
£111 saved.
Reckon the carbon splitters are actually easier to repair than plastic ones. The carbon weave really takes the araldite well, allowing for a better bond.
Cheers