But the Home Office has countered that it isn't technically possible to automatically link or delete records because national and local databases don't talk to each other, and that doing it manually would be too costly to justify.
If you can't do something right, on the basis of it being too costly, that doesn't preclude you from not doing it wrong in the first place. In other words, it doesn't stop the government saying to the police that they should not be permanently recording people's images in the first place, unless they have a good reason for doing so.
As with these new rules the Scottish Government is proposing, you can easily draw a distinction between designing the capability into new systems to remove data once it is no longer needed, and the inability to do so in legacy systems, and thus make sure it is done properly when those systems are replaced or upgraded.
The fact that UK.gov has avoided doing so tells you all you need to know about the data fetishism of both the Home Office and various police forces (I suspect the likes of the Met and North Yorkshire are particularly bad, given their respective track records on respecting Human Rights). I'd like to point out, also, that there is a world of difference between the policies of Police management, and the actions of individual officers, who are bound by those policies. The archetypal bad cop aside, I think a lot of the rot within forces like the aforementioned is in the senior ranks, not the rank-and-file officers, who on the whole do a difficult, underpaid, and stressful job with little recognition in the face of an often hostile public.
Oh, and for those who like to go on about 'unaccountable bureaucrats' it is worth remembering that there are over 300,000 civil servants in the UK (compared to the 46,000 odd employed by the EU), and this sort of fetishism almost certainly originates with the senior ranks of civil servant within the Home Office, and not with Ministers.