HSE Website says "Health and safety legislation applies to all businesses, including third sector employers such as voluntary organisations, charities, social enterprises and not for profit businesses. All these employers have the same health and safety duties as any private sector employer in the same circumstances."
Whether your organisations falls into these specific categories or not I would personally err on the side of caution and say that you should comply with the basic requirements of H&S legislation. As Organisers of events you would be considered to be the 'responsible party' and you shouldn't just rely on the DoC that the venue hosts have.
" We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology " Carl Sagan