well i've taped it up, looking around the internet it has been suggested to use electrical tape because it's flexible, so i used that.
i taped it up then put some rubber covered wire over that so form a tight seal, then i staked the branch in 4 places to hold it up and take the strain off the join. i will losen the wire in the spring and leave the tape on for as long as possible.
i guess i'll only know in the spring if the branch comes into leaf if it has worked, but i hope that because it's a young tree it will pull through