Thanks for the replies.
I took the car back in today and a technician came out on a test drive with me, he was convinced it was down to incorrect wheel balancing (wobble was only there between 56-60mph) so they took the car in there and then.
They did a thorough job this time (aparently out by 5g and not placed correctly)and it now drives perfectly :)
Shame it took 4 attempts to solve it but at least its done now