Have you spoken to your landlord about this? If it's been going on for a year and you've not raised any problems with him up to now he might simply assume you're fine with it.
If the work has gradually spread into your garden, same thing... you've not complained to him and the workmen might not be properly aware of the boundry line.

I'd suggest speaking to him first (if you feel he's approachable), he's next-door so must be sharing most if not all of the nuisances caused by the building site himself.

If that doesn't work.... it's probably time to approach ASLOCA. But be prepared for one very upset and potentially vindictive landlord.