"in a private room at the Mitre for Esme Clay and her husband"

The rather grand facade of the Mitre overlooks the River Thames and was originally used to house those courtiers unable to lodge at Hampton Court Palace just opposite.

The Mitre
Creative Commons AttributionThe Mitre - Credit: Jim Linwood

Aspects of the building date back to 1665.

On a more creative note, "Esme Clay and her husband" appear to be fictional characters created by William Boyd...not some of the many real-life figures threaded throughout the rest of the novel.