Public interest or public task 

Necessary for performance of a specific task carried out in the public interest which is laid down by law, or in the exercise of official authority - for example, a public body’s tasks, functions, duties or powers set out in law.
Vital interests Necessary to protect someone’s life or, for example, if a child or young person is deemed to be at risk of significant harm.
Legal obligation  Necessary to comply with a common law or statutory obligation.
Consent The individual has given clear consent for their information to be shared for a specific purpose.
Legitimate interests Necessary for your legitimate interests or those of a third party, unless there is a good reason to protect the individual’s personal information (cannot apply for a public authority sharing information to perform official tasks).
Contract When necessary in performance of a contract entered in to by an individual and therefore unlikely to be relevant in this context.

Further information on the lawful basis to share information can be found on the ICO website.