On the right is the former General Post Office building designed by Sir Robert Smirke (demolished), on the near left is  GPO West or the Central Telegraph Office designed by James Williams (demolished - the site is now occupied BT ), on the far left is GPO North designed by Henry Tanner (now home to a Japanese banking group)
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/98841101@N00">jelm6</a>
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<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jim6/5280283894/">Postcard view of former post office buildings, City of London</a>