On 11 August 2009, Castle challenged Health Secretary Andy Burnham during an interview on GMTV, after news reports had cast doubts on the effectiveness of Tamiflu against the swine flu virus. He said: "I can tell you that my child — who was not diagnosed at all — she had asthma, she took Tamiflu and almost died." He is the great-great grandchild of Annie Besant, a prominent British socialist, Theosophist, women's rights activist, writer, orator and supporter of Irish and Indian self-rule, and the uncle of Sienna Nasir-Hawkins, the daughter of Chris Hawkins and Clare Nasir-Hawkins.