As flagged by Richard Vines on Twitter, Marianne has shut its doors and its website has been taken down.
Lumb, whose CV includes Michelin-starred Gravetye Manor, opened the 14-cover restaurant five years ago.
She announced in June that she would be leaving the restaurant in August to spend time travelling and cooking in Asia and the Caribbean.
The restaurant was set to stay open with chef Miles Strotton taking over the kitchen.
“It is one of the toughest decisions I’ve ever had to make, but I am so proud of what we have achieved,” Lumb wrote in an Instagram post in June.
The chef reached the finals of Masterchef: The Professionals in 2009 and is currently appearing on Great British Menu.