Hi seastar:
You're well rid of the swine if that's how he treated you. My other half would have been on her toes years ago if I'd ever raised my fist at her let alone actually done anything.
Assuming that you're in England or Wales, your DNA could remain on file indefintely the way things stand at the moment.
In Scotland it would not have been retained under the circumstances you've described.
However, the Home Secretary recently announced that the DNA system, in layman's terms, will be reformed in the not too distant future to reduce the length of time, in most cases, that it can be held on file.
To use your language, yes, "your average pc plod" could theoretically access the fact that your DNA was taken. If, however, s/he cannot justify the reason(s) for doing so, they may commit criminal offences for which thay could be prosecuted.
It is, however, hypothetically possible for someone to innocently know about your DNA details, i.e. anyone with a knowledge of the law who knows you've been arrested? This is perhaps improbable, but still possible.
Hope this helps.