Salt Yard's food hygiene rating of 0 has been described as "an isolated incident".
The Food Standards Agency awarded the restaurant in London's Fitzrovia the lowest rating in December 2017.
A spokesperson for the group said: "The restaurant was inspected back in December where Salt Yard received a low rating unfortunately due to a small isolated incident. Since then, the team have worked very closely with the council in rectifying the systems.
"This is not something the Salt Yard group have taken lightly, and this is an isolated incident within their group. Salt Yard hopes to regain their five-star rating (which they have held throughout previous inspections) in the near future when the inspector returns however unfortunately, it can take three to four months before a return visit."
Salt Yard was opened in 2005 by Simon Mullins and Sanja Morris as a charcuterie bar and restaurant serving tapas inspired by Spain and Italy. The group now encompasses Opera Tavern in Covent Garden, and Ember Yard and Dehesa in Soho.