I too not long ago went through the inheritance gunk with the UK.

> These then need to be 'notarized' by a legal person - with seals and embossed stamps before they can be used to identify me. It's medieval.

My experience of this was they (the insurance/solicitors) were just being obstructionist for fun, because when confronted with the requested notarized documents they kept moving the goalposts around, and only a threat to withdraw business from them on other fronts made them snap out of it.