Geograph - photograph every grid square

A fabulous building which should be better known. Pevsner somehow missed it completely. Information is hard to come by, but it must date from the late 1960s or early 1970s. One would like to know the architect.
Update: BT Archives kindly provided some information. The exchange was built in 1969-72 at a cost of £1.2m as part of the GPO/BT microwave system. The design team was Thomas Winterburn (Senior Architect at the Ministry of Public Buildings and Works), W. Freeman (Senior Civil Engineer), and E.W. Hutchinson (Project Engineer). It was, and possibly still is, known as "the Hadrian Trunk Switching Centre. A trunk switching centre is a particular type of exchange dealing with trunk calls (national calls to, or from, or passing through, the local exchange area)". The land was acquired in 1929 for the General Post Office. The first buildings were constructed in 1932 as general stores, garage and workshops. These were demolished in 1966.