Hi,
You only have to fill in in the Capital gains summary pages (or report your disposals in some other way) if:
(a) you sold or disposed of chargeable assets which were worth more than £49,200
(b) your chargeable gains before taking off any losses were more than £12,300
(c) you want to claim an allowable capital loss or make a capital gains claim or election for the year
(d) you were not domiciled in the UK and are claiming to pay tax on your foreign gains on the remittance basis and have remitted foreign chargeable gains of an earlier year
(e) you sold or disposed of an interest in UK land or property and were not resident in the UK or you were a UK resident and overseas during the disposal
(f) you submitted a Real Time Transaction return on the disposal of an asset and have not paid the full amount of Capital Gains Tax.
If you are non-resident you can find more information in this helpsheet:
Non-resident Capital Gains for land and property in the UK (Self Assessment helpsheet HS307)
Thank you.