Sony will probably ask you to get a repair estimate before deciding what they will do. You can either contact John Lewis directly to see what they say or speak to Sony customer services directly.
I'm in the same boat as you with a similar fault. I had to pay £60 to get a repair estimate and the service centre has confirmed that the LCD panel in my set is fault and needs replacing. I have sent to Sony including proof of purchase along with the estimate and a strong letter. I'm now waiting for a decision regarding what they describe as a "Good Will Gesture" what ever that means..
Check out the various different threads on this forum and others as some people have had some success getting Sony to repair or replace their sets but, I think they operate on a case by case basis.
I'm waiting for the verdict on my faulty set.
Good luck
