The "Holford Rules" are a series of planning guidelines first developed in 1959 by Lord Holford adviser to the then Central Electricity Generating Board (CEGB) on amenity issues. They were reviewed in the 1990s by the National Grid Company (NGC). So far as the Executive is aware the rules are not published as a single work but they are referred to in a number of planning publications including Visual Amenity Aspects of High Voltage Transmission by George A. Goulty (1989) and Planning Overhead Power Line Routes by RJB Carruthers (1987) Research Studies Press Ltd, Letchworth.
The Holford Rules are:
Avoid altogether, if possible, the major areas of high amenity value, by so planning the general route of the line in the first place, even if the total mileage is somewhat increased in consequence.
Avoid smaller areas of high amenity value or scientific interest, by deviation; provided that this can be done without using too many angle towers (i.e. the more massive structures which are used when lines change direction).
Other things being equal, choose the most direct line, with no sharp changes of direction and thus fewer angle towers.
Choose hill and tree backgrounds in preference to sky background wherever possible and when the line has to cross a ridge, secure this opaque background as long as possible and cross obliquely when a dip in the ridge provides an opportunity. Where it does not, cross directly, preferably between belts of trees.
Prefer moderately open valleys with woods, where the apparent height of the towers will be reduced and views of the line will be broken by trees.
In country which is flat and sparsely planted, keep the higher voltage lines as far as possible independent of smaller lines, converging routes, distribution lines and other masts, wires and cables so as to avoid a concatenation or "wirescape".
Approach urban areas through industrial zones where they exist and where pleasant residential and recreational land intervenes between the approach line and substation, go carefully into the costs of undergrounding, for lines other than those of the highest voltage.
The two Scottish grid operators, Scottish & Southern Energy and Scottish Power, have reviewed the applicability of the Holford Rules to Scotland. When this information is available it will be placed in Parliament’s Reference Centre.