By Christopher Watson (http://www.comebirdwatching.blogspot.com/) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Australia. Most of Australia except for a broad coastal belt along the south and east.
Least Concern
NBN atlas has 71 records as at end 2024. Map Here.
Landguard Bird Observatory on the Suffolk coast recorded one on 29th-30th May 1989 and another on 28th July 2017.
Nottinghamshire has had three report, all of single birds, between 1990 and 2001.
An internet search (diamond dove sightings in uk)produces quite a few sightings from up and down the country.
https://www.lbo.org.uk/systematic-lists/systematic-list-of-escapes/