Neighbour has extended into loft above my flat and now has access to my flat

I just wanted to get some advice regarding my options here.

My neighbour has been building an extension above my flat and now the only thing between my flat and his is a flimsy piece of wood that is the loft hatch.

I’ve notified my landlord, but I think it will take him a while to sort out anything in terms of security.

I don’t feel safe knowing my neighbour could access my flat at anytime without me knowing.

Thanks in advance for any advice.

I’m in England if that helps.