The post you are reporting:
I don't see what all the fuss is about, JB. The Prüm convention (data exchange of, e.g. DNA) is open to all EU members; that's the treaty the UK (eventually, after initially opting-out) signed up to. The Schengen Information System is open to participants of the Schengen Agreement; the UK, like Ireland, is not a signatory, but co-operates under the terms of the Treaty of Amsterdam. Likewise the European Criminal Records Information System (ECRIS, sharing information on past convictions). The UK has been shy of fully buying into these agreements in any case, so shouldn't really be complaining. But aside from that, the important point is that countries participate in these agreements by virtue of their EU membership. Ergo, when the UK ceases to be an EU member country its right to be a participant in the agreements ceases also. Presumably any policing and security protocols will need to be re-negotiated, with the UK as a third country, just like all the UK's other arrangements with the EU. Nothing new there.