Minors passport in possession of absconded parent. - England

I am posting on behalf of a friend who isn’t on Reddit. So I’m going to try and be as factual and straight to the point as possible.

I’m not sure if this is the right sub but here goes.

Children both are under the ages of 16. Father (divorced from mother, now very recently remarried) took the children on holiday last year abroad.

Upon return children returned to mum as was normal and within a month or so father decided he wanted no more to do with the children, withdrew child support, blocked them all on social media etc and refused any further contact.

The problem is that dad still has the passports. My friend has been advised that she would need to go through the courts to replace the passports?!

Or is it just as simple as reporting them as lost and reapplying for new?