CGT on house transfer

My son and I bought a house for him to live in in 2013 for £245,000. I was sole "owner" at Land Registry, but had only a 20% financial interest in it with my son having the remaining 80%. This was formalised in a Declaration of Trust in 2014. I have just gifted my 20% share to my son and Land Registry now has him as owner so I have a CGT calculation to make for this. Will a simple RICS valuation survey suffice for CGT calculation? One surveyor has just told me if I want a "legal valuation" they couldn't do it. I asked what this was and then were uncertain as to its' definition. I paid the all the purchase expenses including Stamp Duty but can I allow for all this in the CGT calculation or just 20% representing my share?

Hi howard rowley,
You will need to obtain 3 valuations to take an average and then have your 20% of it to work out your gain.
You can only claim 20% of the stamp duty and other relevant expenses.
Thank you.