Here I have partially reproduced a table, which shows the comparison between the Sheldon Scale and current UK Grading Standards, as printed on the book "The Standard Guide to Grading British Coins" by Derek Francis Allen, available from Rotographic.
Coins above 64 in the Sheldon Scale are usually termed Select, Choice or Gem Uncirculated in the UK, or “in fact anything that differentiates the top-notch from the workaday”, as stated by Mr. Allen. Among dealers there was never a consensus on approved terminology!