Thank you for showing me where to find this, which explains my predicament.
Microsoft Windows [Version 10.0.10240]
(c) 2015 Microsoft Corporation. All rights reserved.
C:\WINDOWS\system32>dism /online /get-intl
Deployment Image Servicing and Management tool
Image Version: 10.0.10240.16384
Reporting online international settings.
Default system UI language : en-US
System locale : en-GB
Default time zone : GMT Standard Time
Active keyboard(s) : 0809:00000809
Keyboard layered driver : PC/AT Enhanced Keyboard (101/102-Key)
Installed language(s): en-GB
Type : Partially localized language, MUI type.
Fallback Languages en-US
Installed language(s): en-US
Type : Fully localized language.
The operation completed successfully.
Well, as you surmised, it is a US ISO, so I am stuffed. I have to download and install the US version, which means my languages will be messed with again.
That would be Dell causing havoc yet again. Every little thing I come across that causes a problem with Windows 10 has been down to them and their non standard installations. They sold me this as a UK Laptop, with a UK Keyboard. Was it cheaper for them to install it using a US ISO? Sorry, just venting.