Whilst the stay in UK restrictions are in place, you are only allowed to leave the UK from England if you have a reasonable excuse.
This applies to holders of UK and non-UK passports.
It is illegal to travel abroad without a reasonable excuse. Travel abroad for holidays is not permitted.
https://www.gov.uk/guidance/coronavirus-covid-19-declaration-form-for-international-travel#permitted-reasons-for-international-travel
樓上條link 有”reasonable excuse”