Neighbour of mother in law has started building his house extension with 2 or 3 metres of her house. He has got a party wall surveyors involved with his neighbour on the other side where they share a wall but not for her. He is also starting to dig out for retaining wall within a metre from her house wall (which is suspect doesn’t have a recognised foundation due to is age 18th century)

https://www.gov.uk/party-walls-building-works/work-tell-your-neighbour-about

I’m pretty sure there should have been a party wall agreement in place before he started, but what can be down now it’s started?

I’m no expert,but I’d have thought that whether or not he’s started has no bearing on the legality of what he’s doing.

Iirc the limit is 3m from an existing building for excavation works.
Look at the party wall explanation booklet.

You can apply for an injunction if the regulations are breached, but that just stops work and if they have finished before it gets granted what do you do? The costs also fall on you if unsuccessful.. gut would tell me if neighbour has got surveyors in and is cooperating with other neighbours correctly then they think they’re correct and have possibly been advised so, so you will likely have to take legal advice first etc before risking it, all time and money.

Notices should have been served if proposed excavation was within 6m of the foundations (s6(2)PWA1996).

I would advise that unless an Award under the Act is put in place you will be applying for an injunction to stop the works and damages for failure to comply with PWA.

You can retrospectively agree an Award. Note that he has to bear the cost of your MIL’s surveyors so she shouldn’t be out of pocket.

When this happened to me I wrote them a letter, immediately, pointing out that they were acting illegally and that I would hold them responsible for any damage from subsidence, etc. At that point they had already dug the full excavation so stopping work would have been counter productive. I also notified Building Control, with pressure from them and me the builders put supports in (which they should have done before) – fortunately the clay remained stable while they completed and backfilled everything.

In the OPs case there may be a greater risk. They are definitely illegal, whether you try asking for co-operation or go to law is up to you.

Cheers, folks, some useful suggestions. My main concern is they have obvioulsy ignored wany they should have done but they really need to crack on and finish the retainiend wall ASAP but then get the paperwork sorted so if she has future problems with settlement or future house buyer searches.

I’l get her to wirte ito them and copyin Building Control to pt them on notice as well.