Here's what Russell said about this conference in his autobiography:
The Pugwash movement now seems to be firmly established and part of the respectable progress of scientific relations with international affairs. I myself have had little to do directly with its progress in the last years. My interest turned to new plans towards persuading peoples and Governments to banish war and in particular weapons of mass extermination, first of all nuclear weapons. In the course of these fresh endeavours, I felt that I had become rather disreputable in the eyes of the more conservative scientists. The Pugwash movement held a great meeting of scientists from all over the world in London in September 1962. I was to speak about the founding of the movement and I warned my friends that I might be hissed--as I was fully convinced that I should be. I was deeply touched by being given a standing ovation when I rose to speak which included, I was told, all the participants, all, that is, save Lord Hailsham. He was present in his capacity as the Queen's Minister of Science. He was personally, I think, friendly enough to me, but, weighed down by office, he sat tight. That was the last occasion on which I have taken public part in a Pugwash conference.(1)
(1) The Autobiography of Bertrand Russell. Vol III, 1944-1969, Simon, 1969, p. 111.