Is it possible to have your children adopted from you without your knowledge?

Can't really think of a more suitable sub, sorry...

I have very vague details, but apparently my ex's husband had his teenage children adopted from him, within the last 5 years and he was never informed at any point. He left Scotland to live in England, so much distance was involved, and different bodies in Scotland compared to England. However we just can't see a way this would have come to pass. He's a nice enough guy, not violent to my knowledge, but he no longer has legal responsibility for his children somehow.

We can't think of any way this could come to pass as they knew where he lived, he was contactable by post... Unless... And it sounds insane but... Unless my ex, who's always worked from home over this timescale, intercepted the mail and binned it. Unless he has a really really dark past, which I'm confident he doesn't I saw his kids visiting once, all fine... Well what else could possibly explain it?