Hi @NeilNorpa ,
Per my research, you could set the UK users' Regional format to United Kindom in My Account. The setting will only change the date formate for the user but not the tenants scope. And the user will get all date format with the locale in the setting.
Here is a nice article for reference
https://pkbullock.com/blog/2020/the-many-ways-to-set-uk-locale-in-sharepoint
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