This happened to me once, ironcically on the day I was being made redundant and was in receipt of two redundancy packages, which made it about £16k in total. My first son was only a month away as well and given that there were two pregnant females that hadn’t even been put at risk, I was pretty angry and came close to just not giving it back at all.
This happened at a national level at one of my previous places, simple admin error meant that redundancy packages were paid twice, the day they left the role, and then again at the end of their 3-month gardening leave date.
I seem to recall about 40 people were ‘the lucky few’ the contracts were complex so even when the first couple of Honest Joes called in, HR couldn’t confirm if they were due the money or not, and asked them to sit on it. When it was confirmed a few weeks later it was an over-payment, the majority of people involved became “uncontactable”.
I think some paid it all back as soon as they were asked, some paid it back in instalments over a LONG time and some disappeared never to be seen again. Legally it’s pretty clear cut, you have to return it – but I doubt the Police would consider it a criminal act or want to peruse it, there’s no credit agreement so you can’t go through the county court, meaning an expensive High Court case would be their only legal recourse.