GGT on gifting a share of my 2nd home to a child.

Hi, I have owned a London flat for 27 years. The first 17 years it was my PPR until I bought & moved to another house which then became my PPR. I rented the old London flat. I bought the London flat for £300k in 1997. It’s now worth £1.3m - so capital gain is £1m to date. If I sold the flat now, I would be liable to 28% CGT on 10/27 of the £1m gain = 28% x £370k = circa £103k. Question. If I gifted half of the flat to my 2 children now (before Oct Budget), would I be liable to pay the full CGT of £103k and would the overall Gain to date then be considered by HMRC to have been crystallised. Hence resulting in any future capital gain from the date of transfer being measured against the new crystallised value for both myself & my 2 children? Or would I only have to pay CGT of 50% on the gain to date, as I was only gifting 50% of the priority? I would much prefer to pay the full CGT now so that any future CGT liability to myself would be rebased against the current value of £1.3m, as I appreciate the flat’s value is unlikely to increase as much as it has done over the past 27 years. So much more economical for me to clear the full CGT slate now, whilst I’m only eligible to pay CGT on 10/27 of the gain. Hope this makes sense, and would appreciate any advice? Thanks.

Hi Peter,
You will be liable to Capital Gains tax if you gift the flat to your children, using the market value of the property. You can claim private residence relief for the period that the property was your main residence, to reduce the gain.  
Guidance can be found at: Shares and Capital Gains Tax (Self Assessment helpsheet HS284).  
There is a calculator at: Tax when you sell property, which follows on to the Capital Gains service, where you can report and pay the Capital Gains tax due within 60 days of the completion date.
Thank you.