Hi mate. I had exactly the same
problem on my 54 plate SE. The drivers seat squeaked everytime you moved in it. went back to the dealers 4 times in all before finally getting sorted. it was a rod in the back of the seat which had become unclipped, simple solution, they clipped the rod back in and secured it. squeak was gone but got rid of the car a few months later for one without any squeaks and rattles. hope this helps