Thank you for your responses.
1 A valuation was carried out in 2008 when 50% was sold and was £135,000 (mortgage company valuer).
2 It seems there was no further valuation done in 2014 but I can't find any paperwork - only a brief spreadsheet I did at the time showing costs ie £Lender £199 admin fee (I took on the mortgage that had been shared), Mortgage agent fee, sol fee. (Can't check with sols as they have been shut down).
3 I had tried to sell the property on the open market in 2018 as my mortgage term was ending and the flat was valued at £135,000 by Reeds Rains. It didnt sell and there was little interest but that is the last full valuation it was given. Will HMRC accept that valuation for 2014. I then tried it with an online auction which was a disaster - priced at £110,000 with reserve of £120,000 and £6,000 fee to seller - no interest at all. At this stage the "cash buyer in 28 days" style companies weren't interested. Eventually the tenant decided to purchase the flat for £90,000 as he knew it was a bargain.
3 Re partner status - non live-in boyfriend of 13 years up to 2014 - boyfriend odd term for a 70 year old but describes the relationship I suppose.
I have done two computation sheets in draft to show how I have arrived at the figures on the summary sheet and yes I have made a loss. So if I submit two computation sheets with a brief explanation as to why, and also explain about the 2014 valuation not being carried out, but valued again in 2018, does that seem acceptable to HMRC.
Thank you for your help.