Houthi top negotiator Mohammed Abdulsalam confirmed the letter’s authenticity to Reuters.
The office of Hawkins, who is himself a British national, did not respond to a request for comment. The US and British embassies in Yemen did not immediately respond to a request for comment.
The Houthi movement controls much of Yemen after nearly a decade of war against a US-backed and Saudi-led coalition. The war has shifted to a no-war, no-peace stalemate as the fighting has largely stopped, but both parties have failed to renew formally a UN-brokered ceasefire.
US and British warplanes, ships and submarines have launched dozens of air strikes across Yemen in retaliation for Houthi attacks as container vessels have been forced to divert from the Red Sea, the fastest freight route from Asia to Europe.
US and British forces on Tuesday targeted a Houthi underground storage site as well as missile and surveillance capabilities, the Pentagon said.