Issue with phone insurance

PHK

flaneurs_lobster said:

There was a tangential thread recently that discussed phone blocking

https://forums.moneysavingexpert.com/discussion/6535765/mobile-phone-blocked/p1

There the OP had his phone blocked by EE 13 months after he had purchased it refurbed from Music Magpie. They were not an EE customer.

Does raise the questions (at least to me):

What is the actual mechanism by which phones are locked? What does "locked" actually mean (a Google brings mentions of black-/grey-/white-listing)?

Who has the authority to lock a phone and on whose instruction?

Is there 1 single register, or a number which are somehow linked? 

If there's a readable source on the subject I'd be grateful, the Wikipedia entry I found was big on history and 10-year old phone theft stats for London but not much help otherwise.
 

Blocking and Locking are two different things. 

The Mobile Phones (Reprogramming) Act 2012 makes it an offence (amongst other things) for a service provider not to block an IMEI when it is reported as lost or stolen. 

To do that they add the IMEI to one of two databases run by the GSMA. 

The same place that checkmend searches. 

Additionally, there is a database that insurers use to record when a loss/theft claim is made on a phone.