Apparently ‘Keep It Up Downstairs’ is among the 450 films in this deal, rumour is that Network will be releasing it on DVD next may.
http://www.screendaily.com/news/uk-ireland/network-distributing-acquires-rights-to-450-films-from-studiocanal-library/5049999.article?blocktitle=Latest-news&contentID=1846
That would leave Private Pleasures, Whats Up Superdoc and Erotic Inferno, as the only Mary Millington feature films yet to be given a legit DVD release. Keep It Up Downstairs hasn’t been seen in the UK since a VHS release in the 1990s and several (heavily cut) TV screenings on the Beep towards the end of that decade.