When searching, it depends on what search criteria you use.

After trying half a dozen different now, I came across a response saying it was something to do with a scam where they "informed" people "that due to new regulations people with unsecured debt of over £5000 can have 70% written off......."

I suppose it'd be one of those things where they'd either try to get you to pay some fee or other up-front or try to get you to "sign up" for something where the fees would only add to your debt.

They're a nuisance anyway and being "International", I can't block them except to block all international calls.