It is often easiest to find opportunities through organizations you are already connected with. Local museums often offer opportunities, although few are well enough funded to provide paid internships.
Many universities run their own schemes, open to their own students. It is a good idea to approach a Head of Department or Tutor for advice. Some degrees expect students to undertake work placements and can help to organise this.
Safety and insurance. Responsible employers will undertake risk assessments for all placements and ensure that volunteers and interns are covered by insurance. If you are likely to work in laboratories, warehouses or with machinery it is important to check this in advance. If you are working outside the UK you should check the health insurance situation, especially as UK citizens are no longer covered by reciprocal arrangements with EU countries. Age limits apply to some schemes. A number of schemes have been temporarily interrupted by COVID-19 but most hope to restart as soon as possible.