The explanatory booklet is asked directly, at question 35, what happens when a building owner starts work without serving a notice. The answer is that the Act sets out no enforcement procedure for that failure. There is no fine, no notice-serving order, and no automatic penalty written into the legislation for skipping the notice stage.

What fills that gap

The booklet points to a civil injunction as the remedy. That means the adjoining owner, the neighbour whose property is affected, would need to apply to a court to have the work stopped or altered.

That distinction matters for how you read anything else you come across about missing notices. A civil injunction is a court order sought by one party against another. It is not a criminal matter, and it does not start on its own the way a fine or a prosecution would.

Section 16 creates offences for refusing or obstructing a surveyor, builder or other authorised person entitled to enter a property under section 8. It also covers the removal of anything, such as furniture or fittings, that stands in the way of that entry once fourteen days' notice of entry has been given. These are the only offences the Act creates.

Failing to serve a party structure notice, a line of junction notice or an excavation notice is not on that list. There is no section in the Act that makes it an offence, and nothing in section 16 stretches to cover it, whatever a letter or a quote might imply.

What that means if work has already started

The absence of an offence does not mean the absence of a remedy. It means the remedy sits outside the Act, in the civil courts, and it takes the form of an injunction.

An adjoining owner (the neighbour whose property is affected by the work) who wants that route explained in full, including where the injunction remedy comes from, can read What Happens If a Party Wall Notice Is Ignored?. Anyone still deciding whether the work in question needed a notice at all can check the excavation distance and depth conditions at Excavation Near a Boundary, or work out which of the three notice types applies at Party Wall Agreements.

Once work has actually started, you cannot undo that with a notice. But you still have options, and they run in a sensible order.

Check which notice should have been served

Before raising anything, work out which notice actually applies to what your neighbour is doing. A new wall at the boundary, work to an existing party structure, and excavation near your foundations each sit under a different section of the Act, with a different notice period attached. You can check which one fits the job on the notice periods page, and if the work involves digging near your foundations, the excavation page sets out the distance and depth conditions that decide whether a notice was owed at all.

Raise it with your neighbour directly

The most direct step is telling them the Act requires notice before this kind of work and asking them to serve one now. Work already underway does not remove that obligation; it just means the notice arrives late.

A surveyor can still be appointed

Section 10(1) sets out two ways to appoint a surveyor: one agreed surveyor for both of you, or one each. Nothing in the Act says this route closes once work has begun, so it remains open even at this stage.

If your neighbour will not cooperate

Where a notice was owed and none was served, and your neighbour won't engage, the remedy sits with the civil courts. What happens when a notice is served but then ignored is a different situation, covered separately, with its own consequence for each notice type.