In March, Collins met Sir James Craig, Prime Minister of Northern Ireland, in London. They signed an agreement declaring peace in the north which promised cooperation between Catholics and Protestants in policing and security, a generous budget for restoring Catholics to homes which had been destroyed, and many other measures. The day after the agreement was published, violence erupted again in the Arnon Street killings. A policeman was shot dead in Belfast and in reprisal, police entered Catholic homes nearby and shot residents in their beds, including children. There was no response to Collins' demands for an inquiry. He and his Cabinet warned that they would deem the agreement broken unless Craig took action. In his continual correspondence with Churchill over violence in the north, Collins protested repeatedly that such breaches of the Truce threatened to invalidate the Treaty entirely. The prospect was real enough that on 3 June 1922 Churchill presented to the Committee of Imperial Defence his plans "to protect Ulster from invasion by the South."