Neighbour Extension advice

[Th1rteen]

We moved into a semi-detached new build 2 years ago. On one side, we have our driveway up to our detached neighbor’s wall. We have minimal but good relationships with both neighbors. Almost 2 months ago, the detached neighbor asked to access our driveway and remove a fence panel temporarily for building work, promising to restore everything.

The work started, and initially, it seemed like a patio, but then they dug foundations and began building a timber frame extension. We went away for the weekend and come home to find the final roof beam now extends over our fence by 5-10 cm, which might increase with slate tiles and guttering. The fence, initially attached to the exterior wall of their house, defined our boundary clearly, as the wall led onto the fence and went straight down the garden. .

After speaking with the neighbor, he mentioned Building Control approved the work on the basis that the eaves of the original roof already overhang the boundary, but he understood our concern and would talk to the builders. I checked our title pack (having some conveyancing knowledge) and found no Covenant or Easement for the original roof overhang. This raises questions about possible flying trespass or incorrect fence placement if the boundary line should in fact be in line with the eaves!

The neighbor has since avoided us, and the builders paused work for nearly 3 weeks, aside from fitting some glass to the front of the extension. Recently, a 'manager' visited, but no update followed, and now the neighbor is on holiday. I'm worried the builders will continue without addressing the overhang issue.

Questions:

1. Should I contact Planning about potential trespass, even though no Planning Permission was needed?
2. If the original eaves overhang the boundary, does this allow the new extension to do the same?
3. Can I deny the builders driveway access if the situation escalates, especially since they still need to install cladding?
4. Am I overreacting about a minor issue?

Thanks for your advice!