Hello, I am a solicitor with over 15 years experience. I will try to help you with this.
The Party Wall etc Act 1996 (Section 6) states the following. If an owner wishes to carry out an excavation whether for a building or otherwise within 3 metres of an adjoining owner's building then if that excavation/building will be as low as or lower than the neighbours foundations or within 6 metres of an adjoining owners buildings the excavation will be as low as or lower than a theoretical line drawn at 45 degrees downwards from the point where the adjoining owners external wall meets the base of the foundations then you must serve one month's notice of the intended works on the neighbour detailing the proposed works and detailing what work s if any are to be carried to secure the neighbour's property.
If your building work fits this definition then you will need to serve notices etc, If not then you will not need to.