So this is a bit complicated,
I am a citizen of both australia and britain,
I have both passports, but my english one expired last year, i now live in thailand but i am moving back to london in mid march. my australian passport is still in date, will i get a visa on entry? or if i take my expried english passport and in date australian passport to show what will they do/say?
i can get a passport over here but its more expencive and ide rather do it in lonon, obviously as soon as i get there i will definately go the the embassy and get a english passport for work etc.
I don't think it matters if you return to your own country with an expired travel document. It's your home, and they cannot deny you entry unless you've been stripped off of your citizenship.
If you enter with your Australian passport, then technically you must leave within 3 or 6 months or you'll have a lot of explanation to do later because you're considered overstaying if you did stay longer than that.
I would do it as you plan to do it. Show both your expired British and your current Australian passport and tell the Brits that you plan to get a new British passport in London ASAP.