Checking up on an ex's new [timesonline.co.uk] partner [guardian.co.uk] is the most obvious use of a new law allowing people to find out [independent.co.uk] if someone involved with children is a registered paedophile [news.bbc.co.uk] (note that it does nothing to detect all the dangerous people who haven't been labelled as such!). So it's ridiculous for the authorities to be feigning(?) surprise at the stats.

When a couple splits up, it's still nearly always the mother who ends up with custody of the kids. And, if she's in love/lust with someone new, she's the last person to have the sense to check up on her lover (especially with the vice of faith/trust being touted as a virtue). Hence, it's no wonder that exiled fathers (and grandparents) make more checks - even without acrimony being involved. However, there can easily be a jealousy and revenge factor too.

Meanwhile, it's also nearly always males who commit such crimes (and crimes in general too). So an incoming male is intrinsically more likely to be suspect than an incoming female, even for the rare cases where the father has gained custody. This should be reflected in the instances where grandparents initiate the check on a new partner. (The reports didn't say whether there's a difference between maternal and paternal grandparents.)

The more interesting situation would be for couples of the same sex. I'd expect hardly any checks initiated by resident or exiled females but also nothing much from resident males, only the ousted males, because it won't be that males have more sense while they're in love/lust with someone new. However, there probably aren't many same sex couples with children at all to be able to get decent stats on those who keep swapping partners.