he renovated and sold. never rented.all inside the 6 years.
i see it as income tax related.
but HMRC want him to give CGT computation.
p.s he has over 80K of interest and interest redemption fees
If your client's intention was to buy property, renovate it and sell it a profit in as short a spece of time as possible, then he has been trading as a property developer. He should get a deduction for his interest charges which would not be the case if the profits were subject to Capital Gains Tax. Maybe that's why HMRC are seeking to tax the profits as gains. It's usually the other way around. You should ask on what basis they feel that CGT and not Income Tax is applicable in this case and appeal against their decision.
I hope this helps but let me know if you have any further questions.