The Ministerial and Other Salaries Act 1975 sets out severance entitlements for Ministers. Severance payments made to Ministers are published in departmental annual reports.
Severance entitlements for special advisers are set out in the model contract for special advisers. The cost of severance paid to special advisers is published annually on gov.uk. The last publication was December 2016 and is available here https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/579892/List_of_special_advisers_in_post_as_at_21_December_2016.pdf.
An updated version will be published in due course.