Well it turns out I had an old 21mm spark plug socket in my tool box that never gets used and is perfect for the job as it has a 21mm hex end for it allowing you to a spanner on the end without having to weld on a nut.
So out came the angry grinder and I cut a 5mm slit in the side of it which allowed me to put the cables into the middle of socket, however one thing I didn't consider prior to doing this was that the cable sheathing may be large than the hole in the centre of the socket, it was. So it mean that when turning the socket it would grab the sheathing and turn that too, so my I though, oh I'll just drill a bigger hole...1 shattered 9.5mm drill bit later and I've come with the tip of drill the hole out first and then cut the slit otherwise the drill bit catches on the slit and if your drill is torquey enough like mine is it will just shatter the bit.
So instead I took the front of the light off and pulled the cable through so that it was just the 4 cables that would go through the socket and not the cable sheathing, this does mean that it's a lot harder to align the lights, so I think I will eventually buy a new socket to drill out first and then cut the slit.
