Standard Telecommunication Laboratories were first established in Enfield, North London in December 1945. Then in 1959 it relocated to purpose-built facilities in Harlow in Essex.

In the mid ’70s around 300 of the technical staff at STL were involved in developing optical fibre communications.

In 1991, the laboratories became a part of Bell Northern Research (BNR), the research arm of Nortel following the acquisition of STC (the parent company) by Northern Telecom, (later to become Nortel)

Photos of the site through the ages

For a detailed history of the site’s development over the years
See Chris Greenhill’s excellent 16 page pdf document
(created for the 2013 STL QCC meeting)

More detailed history of STL by Vi Maile

Nortel subsequently went into Chapter 11 (a chapter of the United States Bankruptcy Code) and was broken up and sold off. All the original laboratory buildings at the Harlow, Essex site, have now been demolished to make way for a science park: KaoPark. The site retains the most recent lab buildings and will provide four large Datacentres.

 And if you can bear to see most of it being knocked down,
here is a Time-lapse video of the site demolition, prior to development:

Wikipedia entry for STL

Booklet on the STL Open Days in July 1967

STL Open Day 1967,

STL Open Day 1967 Small

STL Quarter Century Club website