I'm British and don't need a visa for Pakistan as I have a valid NADRA card. I am coming back within passport validity time as I have return ticket.
For Pakistan, British passports simply need to be valid for the period of intended stay. For those needing a visa the embassies (as opposed to Pakistani immigration) have stricter requirements, but for you only the rules of Pakistani immigration apply. And they only require it to be valid for the perod of stay.