The brick-and-stone building at the corner of Birdcage Walk and Horse Guards Road is often passed by without being much noticed. This may be because in recent years it has been the police station for St James's Park and the few members of the public who have been inside may have had good reason not to want to brag about it. But now that the police are vacating it, because of the government's public spending cuts, we will be seeing more of it, probably as a snack bar or something similar.  This seems appropriate because there was once a coffee house at Storey's Gate before it was demolished in the early 20th century to make way for the Institution of Mechanical Engineers.
The building is not what it seems. It is much bigger than it looks being built like an iceberg with two spacious levels below ground including an emergency exit from the Jubilee Line. Also, it wasn't built as a police station. It was constructed around 1840 by the Office of Works as Storey's Gate Lodge for the park manager almost certainly on the site of a much earlier building used by the Keeper of the Aviaries in the time of Charles 11.
We should be grateful that this was the only addition to St James's Park at the time because in 1856 there was a proposal to build a road and bridge through the middle of St James's Park from Queen Square to Pall Mall involving the demolition of the Duke of York's column.
Edward Storey, one of a family of Storey's who had done work for royalty, was and is, the most famous Keeper of the Aviaries and it is after him or one of his kin that Storey's Gate - and today's eponymous road - is named. Part of his duties was to look after the aviaries hanging from trees along Bird Cage Walk, but he is also credited with "converting the neglected pleasaunce of Tudor times into something like the park as we know it" (newspaper article, 1904).  Edward Storey was married in St Margaret's Westminster 1676 and buried there onn January 30th 1684.