The Calcutta session of the Congress had given an ultimatum to the British Government to accept the Nehru Report or to face a mass movement. Did the British Government accept the Congress' demand? What was its consequence?

No, the British Government did not accept the Nehru Report.

Its consequence was that a resolution was passed declaring Poorna Swaraj (Complete Independence) to be the objective of the Congress and Jawaharlal Nehru was made the president of the Congress.