CH230400 | How to do a compliance check: information powers: rules that apply to all notices: resolving disputes about legal professional privilege: list of working days
From HM Revenue & Customs · Compliance Handbook
A working day is any day except a Saturday, a Sunday, Christmas Day, Good Friday or a bank holiday under section 1 of the Banking and Financial Dealings Act 1971. The Act gives different dates for England & Wales, Scotland and Northern Ireland. All those dates are bank holidays for the purpose of calculating the deadline dates for the dispute resolution process.
As well as all Saturdays and Sundays, the following dates are not working days for the purposes of the dispute resolution process
1 January
2 January (or a substitute day if 2 January is a Saturday or Sunday)
17 March (or a substitute day if 17 March is a Saturday or Sunday)
Good Friday
Easter Monday
First Monday in May
Last Monday in May
12 July (or a substitute day if 12 July is a Saturday or Sunday)
The last Monday in August
Christmas Day (or a substitute day if Christmas Day is a Saturday or Sunday)
26 December (or a substitute day if 26 December is a Saturday or Sunday).