ICR "Unique Identifiers"

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/473745/Factsheet-Internet_Connection_Records.pdf <https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/473745/Factsheet-Internet_Connection_Records.pdf>

> However, without the retention of ICRs, resolving an IP address back to a single user will often not be possible as multiple users may be associated with that IP address. ICRs therefore provide the unique identifier to distinguish between different users of a shared IP address. 
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What?  What?  What is this on about?  I’m guessing it means you need to store whatever the token was that was used to issue an IP number (IMEI, modem MAC, etc), but it’s surely not going to be able to do anyhing about downstream NAT?

ian