Based on the following two links it actually appears you need to be out of UK for seven years !!

All those buying and selling shares in CH should take note if they plan to return to UK


"Mr Simmons, who has lived all his life in the UK, leaves the UK on 5 August 2019.

He returns to the UK on 2 September 2022.

He realises a chargeable gain (on an asset acquired before he ceased to be resident in the UK) of £15,000 on 20 April 2020.

For both 2019-20 and 2022-23 split year treatment does not apply and he was not Treaty resident in another territory in either of these years.

Mr Simmons fulfils all the conditions in TCGA92/S10A*.

2022-23 is the period of return.
2019-20 is the year of departure.
Period A ends on 5/4/20.
The period of temporary non-residence is 6/4/20 to 5/4/22, which is 5 years or less.
He had sole UK residence for at least four out of the seven tax years immediately prior to his year of departure.
A chargeable gain accrues to Mr Simmons in the period of temporary non-residence.



https://www.gov.uk/hmrc-internal-man...manual/cg26565

https://www.gov.uk/hmrc-internal-man...manual/cg26500