Hello and welcome to the site. Thank you for your question.There are changes affecting CGT for non-resident property owners coming into force on 6 Apr 2015.Previously, taking into account your personal circumstances i.e moved to Australia 8 years ago) you would have avoided CGT provided you sold your property whilst being a non-resident in UK for tax purposes. This is changing and from tax year 2015-16, the valuation of property at 5 Apr 2015 would be the base price and any gain over and above that would be chargeable to CGT. You would still be entitled to your gains allowance against this gain and the rest would be taxed.If you were to come back and make this property your main residence again before selling it, then all period the property was your main residence would be covered by principal private residence relief. Additionally, you would get letting relief.To give you a precise number of years required to avaid tax would mean carrying out what if exercise. I have given you an outline.More information on private residence relief can be found here
I hope this is helpful and answers your question.
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