As far as I know the Martlesham Heath was Post Office telephone anologue exchange then BT when it was Nationalised and they ran the NATO comm line from here to NATO HQ in Belgium. They were the second Exchange in the country after London to go Digital in 1980 so they must have been very high priority at the time.
Ideal for Digital computer communication for Comms and sats etc. 
Some info.
http://www.subbrit.org.uk/rsg/sites/f/fylingdales/As well as its early-warning and space-tracking roles, Fylingdales has a third function. It keeps track of spy satellites used by other countries, so that secret activities in the UK can be carried out when they are not overhead. The armed services, defence manufacturers and research organisations, including universities, take advantage of this facility. 
Fylingdales was also an important site in the North Atlantic Radio System (NARS) - a `troposcatter' radio network which connected to the USA via stations at Mormond Hill in Aberdeenshire, the Faroes, Iceland, Greenland and Canada. 
Later a southern link to Martlesham Heath near Ipswich was added, codenamed Project Tea Bag!http://www.connected-earth.com/gallerie ... switching/BT Laboratories, Martlesham (1975) : new ideas, new locationBT Laboratories, Martlesham Heath, after opening in 1975
The British telephone industry has a long tradition of innovation and, in 1975, Queen Elizabeth II opened a new research and development centre at Martlesham Heath in Suffolk dedicated to research and development.
The Martlesham facility replaced the old Post Office research station at Dollis Hill in north London and is now the home of BT Laboratories.
The location was perfect because the surrounding countryside is relatively flat and therefore ideal for testing the radio-based communication systems in vogue at the time. Before the Post Office moved in, it had been an RAF base, used for aviation research during the First World War and later as a base for fighter planes in the Second World War.
Today it is one of the most advanced centres for telecommunications research in Europe. 
It has supported many 'leading edge' developments, including BT's pioneering work on optical fibre technology and submarine cable transmission systems. Now called Adastral Park, it is host to a science park and is one of BT's five satellite earth stations.
System X goes live (1980) : the switch from analogue to digitalLaunch of System X at Baynard House , 1980
The first System X digital exchange was brought into service on July 1, 1980, at London's Baynard House and formally inaugurated in September of that year. This was a tandem junction unit which switched PCM traffic between around 40 of London's telephone exchanges. 
The following year a second System X exchange was brought into service at Woodbridge in Suffolk. This was a 'local' exchange connected directly to customer lines.The development of 'System X' exchanges was the cornerstone of modernisation of the existing network, by replacing analogue exchanges with digital switching centres interconnected with digital transmission links. It enabled an increased variety of facilities and services to be made available to the telecommunications user, resulting in ISDN (Integrated Services Digital Network) and ISDN 2.