The phone network was still largely in Government hands at this point and run by a specialist telecommunications branch within the General Post Office (G.P.O.) - the forerunner to what would become British Telecom. G.P.O. engineers were co-opted into military circles to run phone taps - and as early as 1945, 50-60 warrants a year were being issued by the Home Secretary for phones to be tapped. (Following the Birkett Report of 1957 - the first parliamentary investigation into the reach of the security state - the number leapt to the several hundreds of phone taps by the beginning of the 1980s.)
As well as understanding the potential for phone tapping as a means of gathering intelligence, the military also realised that communications presented a risk of falling victim to unfriendly attacks in a similar vein, or could be vulnerable during a physical attack. In 1956, a G.P.O. paper outlined proposals to create a 'backbone' of physical infrastructure that could be used for secure communications between agencies across the country.
The plan was for a series of microwave towers, roughly 35 miles apart, running along a North/South axis to act as relay points for secure military and government communications - and considered to be of particular importance in the event of war. In fact, Backbone as envisaged would have been of immense cost and doubtful benefit and by as early as 1959 was running into cost difficulties. Despite this, several towers were built - such as at Hunters Stones (by coincidence, close to Menwith Hill and later connected to the base by heavily protected underground cables). As well as military purposes, the towers also doubled up to carry television and radio signals.
Conspiracy theorists have often misread the purpose of Backbone - assuming that it had a direct role to play in signals intelligence of the kind run at Menwith Hill, but in fact it was primarily a communications infrastructure project that fell within the purview of the wider plans for preparations in case of an attack on the UK.
Rapid technological advances during the sixties soon overran the original plans for Backbone and rendered the network largely obsolete.