History
Hertford Heath does not appear to have been a Post Office site but a 1985 planning application by BT sought approval for an "Intermediate Microwave Radio Tower and Single Storey Building" at Elbow Lane (originally part of the Roman Ermine Street/A10 Great Cambridge Road). This appears to be a "take over" site - the 1973 OS map shows "Radio Pylon (Eastern Gas)". The current tower is to the south east of the original and rotated slightly east from north, presumably to simplify the mounting for the BT dishes. From the limited information available it appears BT's building is of the standard pattern for 1980s sites however the tower is not the expected "Type 8A" but a generic "pylon" style.
Initially it was difficult to understand the purpose of this apparently isolated site but the most likely explanation is to allow increased capacity on the London to Norwich and Leeds routes. When the GPO Tower was built it was the general rule to allow approximately 90 degrees separation between routes at any site. This led to a shared section between London and Sibleys via Kelvedon Hatch, ultimately restricting the capacity of both routes. With the more directional antennas available later it became possible to run two independent routes by adding the intermediate station at Hertford Heath and moving the point of divergence back to London. (A similar change was made near Carlisle during the 1970s, adding a site at Wharrels Hill to allow fully-indepenent routes to Belfast and Scotland.)
