Richer Sounds are selling the Linsar 65UHD520 65 inch 4K Ultra HD LED TV with a free Roku Smart Stick for £449 but you can get £50 with voucher code "PAYDAY50".
So that's a massive sixty five inches of 4K screen and a Roku Smart Stick for less than £400. Oh and I forgot to mention it comes with a 6 year warranty (thanks @i_am_sy).
See here https://www.richersounds.com/linsar-65uhd520.html
Linsar is a UK brand whose TV's are assembled by Vestel which is one of the top 3 TV manufacturers in the world https://www.avforums.com/threads/linsar-a-british-success-story.1664855/