The new Tory government in Britain constituted a statutory commission under Sir John Simon. It was set up in response to the nationalist movement, to look into the functioning of the constitutional system in India and suggest changes.
It failed because the commission did not have a single Indian member. They were all British. When the Simon Commission arrived in India in 1928, it was greeted with the slogan 'Go back, Simon'.
All parties, including the Congress and the Muslim League, participated in the demonstrations.