Use the full area code before the local subscriber number.
UK geographic telephone code
01600 area code: Monmouth
The 01600 dialling code is associated with Monmouth.
How to dial Monmouth
Use +44 and remove the leading zero from the area code.
An area-code match describes the number range, not the caller's identity or current physical location. Caller ID can also be spoofed.
Source and review
This page uses Ofcom telephone area codes area-code information retrieved on 3 September 2026.