"Meeting the challenges: Sorting for the Future"

"By the mid 1990s a number of reorganisations of the sorting arrangements for foreign mail had been carried out. There were seven Offices of Exchange (OEs) dealing with export mail. These were Mount Pleasant, Reading, Birmingham, Manchester and Glasgow plus two specialist units – Heathrow International Distribution Centre at Greenford, which handled all the pre- sorted mail posted by major contract customers, and Birmingham ‘Z’ in Sutton Coldfield, which handled all the surface mail. Four OEs handled import mail – the main units being Mount Pleasant and Dover, with smaller volumes at Manchester and Glasgow."

http://www.tmiltd.com/system/includes/images/pdfs/PHTBOARDS.pdf