I discovered I'd got a seized brake piston. I guess this has warped the disc. Refurbished the calipers at the weekend with new seals. They all have a lovely sliding fit now. The steering wheel does feel a bit smoother when cruising but when braking especially from 80+ it's quite a bit worse! . When I checked for warpage by running the car with the front wheels off the ground, of course there were no wheels clamping the discs to the hub. So I expect the pads were holding the discs straight and giving a false impression. I think it must be discs but could it be driveshafts or CV joints?