I won't show you mine if you don't show me yours

So it's come down to this level:

The UK should be denied access to an EU crime-fighting system until it agrees to share more fingerprint data [and DNA profiles] with member states, a European parliamentary committee has said...“We would like the UK to move our way …[indeed] ... to move forward to European Union standards for the sake of building up a future relationship that is mutually beneficial and thus not giving any space for the advantage of not being a member of the European Union [leavers must be punished] and yet enjoying all the information tools.”

British government officials say the UK makes huge volumes of data available in comparison with other member states....British authorities are sharing DNA data from British-based criminals, but not criminal suspects, although it gets full access to equivalent data on suspects from other EU countries...In recent months MEPs have condemned British authorities for failing to pass on details of 75,000 convictions of foreign criminals to their home countries, while accusing the government of “deliberate violations and abuse” of a vast EU database used by police and border guards across Europe.

the system has also come under fire from civil liberties campaigners, who say there is a lack of democratic oversight.

any decision to cut the UK out of the existing DNA sharing agreement would see EU law enforcement lose access to the UK’s DNA database, which holds profiles of more than 5 million people and 500,000 samples from crime scenes.  

The links are interesting, and it is not at all easy to choose sides, of course. The failure to pass on details was reported in January:

The UK has failed to pass on the details of 75,000 convictions of foreign criminals to their home EU countries and concealed the scandal for fear of damaging Britain’s reputation in Europe’s capitals, the Guardian can reveal....The police national computer error, revealed in the minutes of a meeting at the criminal records office, went undetected for five years

Minutes of an ACRO criminal records meeting last May – deleted from the ACRO website after the Guardian story was first published – state: “There is a nervousness from Home Office around sending the historical notifications out dating back to 2012 due to the reputational impact this could have.”

The offical story from the UK, opting as ever for incompetence over deliberate policy is:

“The issue arose when it was noticed that not all relevant DAFs [daily activity files] were sent to ACRO, for example in cases where the subject had dual nationality...“As a result, a software script has been developed at Hendon, the PNC headquarters, and is due to be released in the next software update schedule (the date of which is yet to be confirmed).”

The scandalous deliberate violations and abuse were reported in a Graun story also  in January:

[British authorities] are basically only interested in people coming into the UK,” ... “People going out of the UK – if there is an alert, they are not warning the European authorities, so we are not safer.”...the EU concluded that British authorities had made “unlawful” full or partial copies of the SIS database. The report said “major deficiencies in the legal, operational and technical implementation of SIS” in the UK ...had not been remedied, despite concerns first raised in 2015. The litany of problems pose “serious and immediate risks to the integrity and security of SIS [Schengen Information system] data”...[although an EU official] dismissed claims that the US government had access to the EU database via the UK’s illegal copies. 

Asked whether the database issue could be a problem for Brexit negotiations, [Ms] In ’t Veld [Dutch MEP, same one as in the first story] said: “I very much hope so,” adding that the report showed “violation upon violation”. She added: “If [in 2015, the UK] didn’t care about the rules then, how are we going to make them respect the rules if they are not in the EU any more?”

The question surely shows the problem though? We didn't respect the rule when we were in the EU -- so staying in wouldn't change anything? She just wants to punish us, as usual?