overstayed tourist visa

Hi wondering if anyone can help.

I have overstayed my Australian tourist visa but I'm looking to leave the country. I have booked flights out of the country (to Thailand) and was wondering if i'll still be able to get on these or do the Australian immigration send me back to the UK?

I have been told by someone they will let me go to thailand because I have booked these flights and I am leaving the country not to return. But, someone else told me they'll deport me straight back to the UK.

does anyone know? I do know that if you dont have flights booked they deport you straight home but is it different if you have flights to another country already booked?

thanks...