You need to add a Dial Pattern to your Outbound Route that will accept numbers beginning with +. If necessary, the pattern should rewrite the number to a format that your trunk will accept.
As a guess, try
match pattern: +X.
It’s likely that the +447 number was shown as the caller ID, saved in the phone’s history and being used to redial. If that’s the case, you may want to set up your inbound processing to rewrite incoming numbers show they will display on your phone as 07.
(The above assumes that your server and all extensions are in the UK.) If you have locations in multiple countries you may want to set up a system where all numbers are shown beginning with the country code.)