Apparently, it costs £4pm for UHD.
Some accounts have an offer available where, if you take Disney+ at £5.99pm, the UHD becomes free. The free UHD means that, if effect, you get Disney+ for £1.99pm
You will be billed for Disney+ as normal at £5.99, but taking this service makes the £4 UHD charge disappear on the selected accounts.