i know when you leave the u.k you need at least 6 months in your passport to be able to board your plane and travel to most countrys ,

but if your in another country for a long time how much time do you need in your passport to travel

BACK to the u.k ?

You could actually enter the UK on an expired UK passport, that's assuming the carrier would let you travel.

i asked my opening question because i dont know the "score" about the law and passports but even i would,nt go to the airport with an EXPIRED passport and to expect to board and fly ,

You are a British Citizen and as such have the right to enter the UK, a passport is little more than proof of identity and nationality, expired or not.

There are no rules to say that a UK passport holder needs to have any validity left on their passport when passing through the UK Border.