Salmond says in his resignation speech that Cameron has broken a campaign promise made by Brown:
I spoke to the Prime Minister today and, although he reiterated his intention to proceed as he has outlined, he would not commit to a second reading vote by March 27 on a Scotland Bill. That was a clear promise laid out by Gordon Brown during the campaign. The Prime Minister says such a vote would be meaningless. I suspect he cannot guarantee the support of his party.