Seems like they're still charging £6 for Full HD and £9 for UHD (although in fairness they usually have promotions on so you're rarely paying full price).I'm not surprised. They can't justify charging for 1080p now so they've switched to gouging for UHD instead.
My old TV used to upscale automaticallly and with good results. It sadly died and my new TV doesn't upscale and Netflix immediately wanted to charge an extra £4 per month for 4K. Nope, I'll manage, thanks