Unclaimed pension of deceased dad. Can we claim it.

Hello. Thanks in advance. (England)

My dad died and he was terrible at life admin. He lived off his good NHS pension but never claimed his state pension. My brother and I were helping him get his decree nisi as he divorced years earlier. This would show he was single and determine his payments.

Is there a way for us to claim this as it will be a large lump sum that he paid into?

Thanks.