They mentioned Headway and the CTC debating the helmet issue on radio London and if this helped Headway to understand the issue any better I cannot say. My impression is Headway would not really know where reports were reliable and where they were misleading, eg DfT report RSRR 30 mentions a report from Western Australia, page 49, Table 2, it says
Participation in bicycling remained steady for most of survey groups, except primary school children and recreational bicyclists - fall of 21%.
The report actually mentions a 39% drop for recreational cyclists and a 39% drop for country primary school children. Legislation was introduced in January 1992 and enforced in July 1992, but the surveys referred to were conducted in Feb/March 1992, ie without police enforcment (fines) measures, some cautions were issued. By omitting this level of detail the DfT report effectively misleads and Headway could also be misled unless it had the actual report to study in detail.
Protesting directly at Headway Conferences seems worthwhile as their main supporter may become aware of problems and question the approach taken and information referred to. Alternatives to helmets to reduce accidents and head injuries could be a worthwhile option for Headway to follow, possibly the CTC could provide an 'alternative list'.