If you are non resident then you are not chargeable to UK tax.
Comments like this are scary!
While that might be a generally true statement, on a UK tax forum with an OP that starts
Hi I bought my house in 1984 for 25k
Lived in it as my only home until 2002
Started renting it out in 2002 and became non resident at the same time.
That is a pretty far out assumption that the property isn't in the UK.
The fact that there has been so much hoo-hah about huge penalties for failure to file a NRCGT tax return over the last 7 years even when the tax due is zero, it's... well, I'm lost for words.
I think (and the OP would be well advised to take my comments with a pinch of salt too) that there are at least three different ways that the OP can calculate their taxable gain and can chose the one that will incur the least tax - and I suspect they will give wildly different amounts of tax due too so worth checking all of them, but it seems unlikely that the OP won't have to deal with NRCGT at all even if just to fill in a form and submit it on time.