An approach I'd suggest:
You have listed about a half dozen things that are bothering you. Before going to the Council or Committee that has oversight power, list (write out) each and every issue. Rank them with 1 being the worst, the last on the list being the least important. Don't leave any issue out.
For each issue, what bothers you and why? For example, with the constant drilling described, is it just the noise? Or are you worried that the next structure might be a "tiny home" dwelling/weekend retreat or kiddie park/playground?
If you know other long-term plot holders well, gage their opinions about your new plot neighbor's activities, and their willingness to join in speaking up.
Do you know a "friendly ear" on your allotment Committee? You might want to explain your concerns to that one person first. Offer to meet at the allotment. Try to gage what issues you would get support on, which ones you won't. One thing to consider is whether you can live with some things on the bottom of the list if the issues at the top of the list get addressed.
If you think it would be more appropriate, offer to your Committee to take your concerns directly to the new plot holder (polite and business-like). It's fine to skip this if you think the new plot holder might react badly (threatening/violent etc.).
If all else fails, take your concerns to the full council. If no action, it might be time to look for a new allotment.