Harpenden sits in St Albans City and District, and the council states the rule in its own words: "If you live within a Conservation Area and wish to cut down, uproot or prune a tree you must give the Council six weeks' written notice before carrying out any work." On its Tree Preservation Orders page it adds that determining an application for works to TPO trees can take the council up to eight weeks and that appeals go to the Planning Inspectorate within 28 days. On penalties the council names a maximum fine of 20,000 pounds per tree for the wilful destruction of a TPO or conservation area tree. gov.uk guidance distinguishes destructive offences from other contraventions and explains that penalties can include an unlimited fine. The amount that applies turns on the offence and the court. Harpenden is one of the district's 19 conservation areas.
The district also runs a fast track service for order applications and conservation area notices, with a decision "by the end of the 4th week after validation", available only through the Planning Portal, with the request made within 5 working days of the acknowledgement email and site access during the four weeks. The fast track decision is subject to the council's own terms, including referral to a Planning Committee.
Nationally, gov.uk describes the requirement for "people to notify the local planning authority, using a section 211 notice, 6 weeks before carrying out certain work on such trees, unless an exception applies", and says the work may go ahead sooner where the authority gives consent. gov.uk also states that consent "is needed for carrying out work on diseased and/or dying trees unless some other exemption applies", so a dying or diseased tree is not automatically exempt. Dying on its own does not establish a statutory exemption. We would put the council's page and the national guidance side by side and show which control applies to the work.
We would explain how you check the conservation area boundary, any tree preservation order and the proposed work before confirming whether a section 211 notice or consent is needed.