Hi,
When split year treatment applies, the general rule is that you would only be charged to UK Capital Gains Tax (CGT) on gains arising in the UK part of the split year. It is therefore quite possible that you will not be subject to CGT on disposals you make before 1 June. As you appear to have previously been UK resident however, you should consider the rules that apply to disposals made by 'Temporary Non-Residents', which are outlined below:
Temporary non-residents and Capital Gains Tax (Self Assessment helpsheet HS278)
CG26500P - Capital Gains manual: individuals: effects of residence and domicile for departures on or after 6 April 2013 and general rules from 6 April 2013
If you meet the conditions for temporary non-residence, then gains made during that period of temporary non-residence are treated as arising in the tax year of your return to the UK, which in your case will be 2024 to 2025. These will be subject to CGT.
HMRC considers that the share identification rules apply when the transactions place, whether you are UK resident or non-resident at those times. You can see guidance here:
CG51550P - Capital Gains Manual: Shares and Securities: Share identification rules: Share identification rules for capital gains tax
These include the 30 day rule you refer to:
CG51560 - Share identification rules for capital gains tax from 6.4.2008: the “same day” and “bed and breakfast” identification rules
An exception to this is that the 30 day rule does not apply when the person making the disposal was non UK resident at the time of their acquisition. You can see the guidance here:
HS284 Shares and Capital Gains Tax (2024)
Thank you.