Turns out you could even argue the 20 year service mark isn't a requirement for this medal, they allude to in the covering letter for the Royal warrant that it will be 20yrs to match other services, but if it isn't written down in the RW, is very much open to interpretation. This is a very, very loose Royal Warrant. I know people in the prison service are trying to challenge this, I'd imagine the police wont be far behind given the BF, Police and Prison are very much bedfellows in this (i.e. use of powers, detention, use of force, serving legal documents etc.)
Royal warrant for Border Force and Immigration Enforcement and National Crime Agency Long service and Good Conduct Medals - a Freedom of Information request to Home Office - WhatDoTheyKnow
Further confirmation of aggregated service included below from another FOI.
67821 G Loughney Response.pdf (whatdotheyknow.com)