Google Adwords Team announced on Facebook about Local forwarding numbers are now available for numbers based in the UK.Local Google forwarding numbers share the same area code as your business phone number, or a local area code for the same geographic region. For example, if your business is based in London your ads are eligible to use a “20” area code with your Google forwarding number. If you’d like to show a local Google forwarding number with your ad and already have a local phone number assigned to your call extension, you’re all set. If you’ve assigned a toll-free number to your call extension and prefer to use a local Google forwarding number, update your call extensions settings.
In some cases, a local Google forwarding number may not be available. If this happens, your ad will continue to show a toll-free Google forwarding number.
Read More here about How you can implement it.