Can a Neighbour Build on Land I Own?

There are different cases to consider when determining whether or not your neighbour can build on your land:

Ground Floor Extension

Consent for New Party Wall: you can consent to your neighbour building a new party wall and foundations on your land for the ground floor extension.

Foundation Construction: generally, foundations for a ground floor extension should not extend past the boundary. You can however use eccentric foundations instead which isn’t necessary but it’s an option. Consent will be needed to lay special foundations, though.

Loft Extension

Shared Ownership of Party Wall: in the case of loft extensions, they have the right to increase the height of the party wall thanks to shared ownership under the Party Wall Act. The entire width of the party wall is considered shared, so there are no specific limitations on allowing them to raise it.

Basements and Underpinning

Underpinning the Party Wall: if they plan on doing a basement project then they have all rights to underpin and protect the party wall's foundations. This includes placing new foundations (or underpinning) beyond the boundary. On your side you’re also allowed to underpin with some restrictions, especially if reinforced concrete is used.

Overall Conclusion

The rights listed above are subject to certain circumstances and legal considerations. While there may be some permissions, any construction done on your land should generally require your approval. However, when it comes to reinforced concrete foundations, explicit approval is required due to its nature. These topics are typically outlined in the Party Wall Act which sets the legal framework for such projects.