The artist Carrie Reichardt is part of this group, probably its main artist, "Mad in England" being her trademark.
2018: Via Facebook Carrie kindly confirmed that she had made this series for a commission for the Whitecross Street Art Party many years ago. We found some references to this event in July 2010 so, if it was a one-off, that must be the year that these plaques were erected.
2021: Since then we have found other English Hedonist plaques widely distributed across London. We think this EH is midway between history and an on-going art installation.