M&S wants to demolish its current Art Deco building near Marble Arch and build a new store, along with offices, an arcade, a cafe and a gym.
Matthew Fraser, on behalf of campaign group SAVE, told the hearing the retailer's "threat" to leave its flagship store "if they don't get their way" was "not the constructive attitude of a retailer committed to the future of Oxford Street".
"This could be avoided if M&S "seriously and creatively" consider the option of refurbishing the buildings.Image caption,Mr Harris told the inquiry refurbishing the existing buildings, which date back to 1930, was "undeliverable and unfundable". The retailer's plans were given permission last November by Westminster City Council, which said the new store would be important to the future of Oxford Street.Barrister Sioned Davies, speaking on behalf of Westminster City Council, which supports the scheme, said any new building would not harm the local heritage.