Wimpole Street Post Office
This was at the southern end of Wimpole Street, on the east side. The Royal Society of Medicine website tells us: "Once again 1 Wimpole Street was given a major refurbishment between 1982 – 86 .... The existing premises were extended onto the site previously occupied by the Western District Post Office." And we see in Google Streetview they had another massive refurbishment in 2012.
There is a picture on Flickr, all rights reserved.