(HPA) was formed in 1943 in order to look after the interests of medical physicists employed in the NHS. It was both a professional organisation and trade union until 1987, when the Institute of Physical Sciences in Medicine (IPSM, now IPEM), was formed to deal with professional and scientific issues. In 1993, the HPA joined the Manufacturing, Science and Finance union (MSF), which has subsequently amalgamated with the AEEU to form Amicus. This gives the HPA access to greater financial, political and service resources.

HPA members at each workplace elect an accredited representative who is officially recognised by the management of their particular trust and can therefore take part in local negotiations.

Every year, usually in September the HPA holds its annual delegates conference. The delegates are elected from amongst the HPA members in a specific region. The delegates are encouraged to express the views of their local members on various issues raised by the HPA executive. Regions can also present motions on topics of particular interest to them at this conference. The day also has time for some workshop activities on issues likely to be of interest to members as well as some informal time during the day and evening. The ADC is an increasingly important event as it provides the Executive with a valuable opportunity to obtain the views of the members.