The chain drafted in advisers on Friday as it looked to push the company into administration, a move that would affect around 2,000 staff.
Azzurri, which runs Ask, Zizzi and Coco di Mama, confirmed that its 300-plus sites will shut their doors temporarily from Thursday.
The Restaurant Group will close between 75 and 90 sites in its leisure business, which includes the Frankie & Benny’s and Chiquito brands.
Scientists producing a protein "literally born out of thin air" say the product will be a price competitor to soya within this decade.
The research flies in the face of previous studies.
The group said it plans to let a number of Chiquito and Frankie & Benny’s leases in ‘unattractive locations’ wind down.
The owners said an ‘eye-opening’ fishing trip had led them to close the restaurant.