The only people who can link a mobile phone number to a user are a very limited number of staff at the company that the user has a contract (or pay-as-you-go plan) with. (If the phone is an unregistered phone on a PAYG plan, even they won't know the name of the user).
The 'authorities' (e.g. the police, security services and HMRC) can only get that information from the company through a court order. The only other way to get the information (assuming that the phone is not an un-registered PAYG handset) is to find out which company the number relates to, to find out which members of their staff have access to confidential data, and then to pay them a very large bribe. If you get found out, both you and the company employee will face very long prison sentences.
Chris