Agreed, sorry for being unclear, my understanding of the situation is
The CGT in the UK has been reset as at the 5th April, so whatever you paid for the house is irrelevant. You need to understand the valuation of the house as at this date eg. House valuation as at 5th April = 400,000, House sale price = 410,000 means a capital gain of 10,000 which is taxed appropriate to your tax band. If you sell it at the same amount as the valuation then there is no taxable benefit.
The CGT in Oz is as follows; IF the house in the UK was your last primary residence and you have not purchased property in Australia, then you have 6 years from the point at which you last resided in that house before there is a capital gain due.
Both the above are appropriate to my situation but in cases like this I thoroughly recommend taking expert advice.