The Government Centre for Information Systems.
(Originally "Central Computer and Telecommunications Agency").
CCTA is part of the Office of Public Service and Science, which works to improve government's services to the public. They are responsible for stimulating and promoting the effective use of Information Systems in support of the efficient delivery of business objectives and improved quality of services by the public sector.
CCTA had to change its name as it was not an agency in the "Next Steps" sense.
The letters were retained as customers were familiar with them.
Address: Norwich, UK.