Thank you for your question.
Changes to CGT on sale of residential property by non residents came into effect on 6 Apr 2015.
Prior to that, in most cases, non UK-residents paid no CGT in the UK on disposal of a UK residential property.
The HMRC advisor gave you correct advice.
You may find this document helpful .. HS278
I hope this is helpful and answers your question.
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Thank you for your reply.
If you are non resident then any gain from sale of property is not chargeable to UK CGT and you don't have to report it.
SA108 is Capital gain tax summary and SA109 covers residence and remittance basis
Disposal date is completion date and not exchange date.
I hope this is helpful.