It doesn't require ID but is verified against other records and against the electoral register in other regions, i.e. you can't register in two different places. When housemates have moved out I have received letters asking me to re-confirm who is living in the house for the electoral register.

> I think this is a big part as to why postal voting fraud happens.

It might happen, but it is exceptionally rare. The impact of introducing voter ID laws would cause a far larger decrease in election validity due to voter suppression than postal voting fraud causes.