Britain's spy agencies will reveal its knowledge of alleged Westminster-related child abuse at a public inquiry amid concerns it aided in an establishment cover-up. MI5, MI6 and GCHQ have given their full cooperation" with the Independent Inquiry into Child Sexual Abuse, lead counsel Andrew O'Connor QC told a preliminary hearing on Tuesday. Some of the evidence the agencies will give may be heard in private due to national security reasons. All three agencies have already provided files and documents relevant to its investigation into the alleged failure to pursue and prosecute child abusers in Whitehall and parliament. Parliamentary whips have also provided documents and archives to determine its involvement in the suspected cover-up. Mr O'Connor said a number of other notorious cases linked to Westminster - including those of the late former MPs, Cyril Smith, a Liberal, and Victor Montagu and Peter Morrison, both Conservatives - will be investigated. Further allegations ... are also expected to be explored. Allegations stemming from claims that police officers were "warned off" investigating cases of child sex abuse committed by senior politicians and other establishment figures in the 1960s, 70s and 80s will be looked at. The inquiry will also examine why the high ranking diplomat Peter Hayman, who died in 1992, escaped prosecution for sending obscene material through the post. The allegations against Hayman, who is believed to have been an MI6 official, were made public under parliamentary privilege in 1981.