It is obvious that O’Callaghan (of Dublin Fame) thought that he could demolish Archers and then submit a planning application using Cumberland House’s 7-8 storeys as the height precedent.
He obviously thought that Heritage groups wouldn’t really care about a deco building as their primary focus historically has been buildings built pre 1900.
At the end of the day, Archers was copied reasonably well and O’Callaghan only got 4 storeys in the buildings curtillage.
It proved to be an expensive miscalculation, although he did secure IIB to occupy it, I doubt they would have gone for the rest of the scheme without the prestige Facade of Archers even if it is a re-instatement.
It is even possible that he would have gotten a higher quantum of floor space if he applied to retain archers and instructed his architects to design a very symmetrical and sympathetic (wrong word I know) building, Art Deco is a licence for creativity in my opinion not a hindrance.