Unnecessary cost and hindrence to those carrying out works. As adjoining owners can not stop conversion going ahead it just makes work for happy Building Surveyors.
This act can cause lots of problems if owner of adjoining house is not resident. They can cause delay to works without having to give a reason. They can then delay access to their property through not responding to their appointed surveyor.
The cost of suveyors, and possible court action if access denied, is all picked up by home owner trying to do their loft.
The adjoining owner can not stop works so why involve surveyors, courts, etc. All very unnecessary.