I know this has been asked a number of times but could Alan Collett please put my mind at rest!

We are leaving our house in London (this has been our main residence for 10 years) and will be renting in Sydney from September. Our London house will be rented out for 6 months and hopefully will sell within a year.
I know that we will be liable to tax on the rental income minus expenses such as mortgage interest.
Will we be liable for any capital gains tax if we sell. I have been advised that we will be liable if we sell for an amount higher that the value when we leave.Is an estate agent valuation sufficient fot the ATO.

provided you do not purchase a main residence in Australia you will be able to claim a six year absence period from your property. no tax will be due when you sell (provided that you do not claim another property as a main residence).

An estate agent valuation is fine - keep the evidence.