Yes I would agree the +4470 numbers are a major red flag when it comes to scams!
Personal forwarding phone numbers are easily recognized, and they are a major red flag when it comes to identifying scams or scammers. The number is often given in the format +447024013818. The country code, (the +44) seemingly indicates that the number is UK-based number. The 70 prefix, however, identifies it as a personal forwarding number. Because of the high rates charged for the caller, legitimate UK businesses would not be eager to use a +4470 number as a contact number for customers or people applying for employment.
If anyone is given a +4470 number to ring during an exchange of e-mails, chances are you are dealing with a scammer. This is especially true if that number claims to belong to a barrister, lawyer, travel agency, visa agency, lottery claim office or human resources/employment department. Others may correct me if I'm wrong but I have not heard of a legitimate 4470 number.