The NHS Leadership Academy offers a free self-paced online introductory leadership programme, the Edward Jenner programme. The programme is intended to lead to further study, however, can be taken as a stand-alone course.
OpenLearn from the Open University [OU] offers access to free online modules in Business and Management, from Introductory to Masters Level. You need to register on their website to use these materials.
A number of universities offer management courses as MOOCs or Massive Online Open Courses. These courses can be free or require a small fee. They typically offer a certificate of completion if you finish the programme. Courses typically last 2 -8 weeks requiring 4 - 8 hours a week study time. All materials are usually provided as part of the course package. Courses may require you to complete some form of online assessment. Major providers are listed here: