The food critic, 51, was announced by the BBC as Gregg's replacement in December after he was axed due to a series of complaints about his alleged behaviour.
The MasterChef star, 60, stepped down from the programme five months ago while complaints from 13 women about historical allegations of misconduct were investigated.
One-time grocer Wallace, 60, stepped away from the show in the wake of a number of allegations that he had indulged in sexist banter and harassed contestants. He denies any wrongdoing.
The former MasterChef host, 60, stepped down from hosting the show with Jon Torode in November after multiple complaints of inappropriate behaviour on set.