question: What is the name of the person that Churchill did not respond to until December?
context: Roosevelt regarded this offer of a joint project as sufficiently important to have the letter personally delivered by Frederick L. Hovde, the head of the NDRC mission in London, but Churchill did not respond until December. He assured Roosevelt of his willingness to collaborate, and informed him that Hovde had discussed the matter with Sir John Anderson and Lord Cherwell, as Frederick Lindemann was now known. The MAUD Committee had considered the issue of collaboration with the United States, and had concluded that while pilot isotope separation plants could be established in the United Kingdom, full-scale production facilities would have to be built in the United States. The British expressed concerns about the security of the American project. Ironically, it was the British project that had already been penetrated by atomic spies. John Cairncross had given the Soviet Union a copy of the MAUD Committee report. Although not conveyed to the Americans, the British had other concerns about what might happen after the war if the Americans embraced isolationism, as had occurred after the First World War, and Britain had to fight the Soviet Union alone. The opportunity for a joint project was therefore missed. British and American exchange of information continued but their programmes remained separate.
  The Tube Alloys Directorate considered whether Britain could produce a bomb without American help. A gaseous diffusion plant to produce 1 kg of weapons-grade uranium per day was estimated to cost up to £3 million in research and development, and anything up to £50 million to build in wartime Britain. A nuclear reactor to produce 1 kg of plutonium per day would have to be built in Canada. It would take up to five years to build and cost £5 million. The project would also require facilities for producing the required heavy water for the reactor costing between £5 million and £10 million, and for producing uranium metal, which would cost another £1.5 million. The project would need overwhelming priority, as it was estimated to require 20,000 workers, many of them highly skilled, 500,000 tons of steel, and 500,000 kW of electricity. Disruption to other wartime projects would be inevitable, and it was unlikely to be ready in time to affect the outcome of the war in Europe. The unanimous response was that before embarking on this, another effort should be made to obtain American co-operation.By March 1943 Bush and Conant had decided that British help would benefit some areas of the Manhattan Project. In particular, it could benefit enough from assistance from Chadwick and one or two other British scientists to warrant the risk of revealing weapon design secrets. Bush, Conant and Groves wanted Chadwick and Peierls to discuss bomb design with Robert Oppenheimer, and the construction company Kellogg wanted British comments on the design of the gaseous diffusion plant it was building.
answers.text: Roosevelt