The overall picture will be superior on the LG. Whether it's worth the extra £500, only you can decide. If it was for movies, I would wholeheartedly recommend LG over Sony.
I saw both of these TVs about a week ago in Currys / PC World, but only with a 4k demo input. Both looked absolutely excellent (as did the Samsung QLED). John Lewis can demo all three with SD and HD signals from an aerial, and I intend to have another look in the near future. Sony's upscaling has historically always been excellent, not sure about LG.
Image retention would be my main concern (along with panel longevity), and there are some long term tests being conducted here by Rtings: https://www.rtings.com/tv/learn/permanent-image-retention-burn-in-lcd-oled