Actually I think I got it wrong, the squeak came back next time I used the car so I jumped in the back to try and sort it once and for all, it was coming from the back seat on the drivers side but I couldn't understand why. I decided on a whim to grease the rear lockinocking mechanism but wasn't to confident it would resolve the issue but to my surprise it has. I have been squeak free for the last week and I really have tried to provoke it to come back driving over rough roads and speed bumps but it has gone and good riddance.