Since the Government published its Productivity Plan earlier this month, the more eye-catching proposals for planning reform have been the subject of extensive commentary. Plans to create a “zonal system” for the development of brownfield land, for example, have been widely discussed, as has the notion of introducing housing into the regime for infrastructure planning.

Meanwhile, other measures have received less attention. One of those is the somewhat bizarre proposal to allow the upward extension of buildings in London without planning permission.

Such a measure would apparently create permitted development rights to allow vertical extensions. These would be limited to the upper height of “an adjoining building” and apply only where “neighbouring residents do not object.”

The purpose of the changes is to help London to “build up” and thus reduce the need to “build out”, “helping to provide homes for Londoners while protecting the countryside”.

This is a laudable aim, but the proposal raises a host of questions.

First, the common purpose of permitted development rights is to provide a procedural shortcut for development that is acceptable in principle. But it is far from clear that this proposal will provide such a shortcut. This is not only because of the consultation that will be necessary in order to allow “neighbouring residents” the opportunity to object, but also because it seems highly unlikely, given the climate in which most applications are received, that no such neighbours will do so. Given that local hostility towards development proposals is so typical, a measure that confers development rights only in the absence of a single objection is likely to be academic in all but the rarest cases.

Second, it is not clear how the measure will address the range of complex environmental factors that might arise independent of neighbour considerations. The most obvious is the protection for important views of the London skyline; there is no indication how this and other issues will be dealt with.

Finally, and whilst at the moment the measure remains in its barest outline, many in the industry – the London boroughs in particular – will be keenly awaiting further detail on some important questions: what category of neighbour will be notified, and entitled to lodge a terminal objection? How will the height limitations work in practice – what if, for example, adjoining buildings are different heights? Will there be a prior approval procedure to deal with matters such as external appearance (often important to conserve local character) and fenestration (to protect privacy)? We await further detail on these and other important questions.