If you have concerns about a candidate's fitness to practise you should follow the advice at paragraph 25 of Good medical practice.
Spring v Guardian Assurance plc and others . The principles in Spring v Guardian Assurance have been found, by extension, to apply to statements made or information provided after the employee has taken up his or her new position (McKie v Swindon College  EWHC 469).
Kidd v Axa Equity & Law Life Assurance Society plc, Allied Dunbar Assurance plc 
This includes your views about a colleague’s age, colour, culture, disability, ethnic or national origin, gender, lifestyle, marital or parental status, race, religion or beliefs, sex, sexual orientation or socio-economic status.
Saha v GMC  EWHC 1907
You should also consider the impact of the data protection law on the disclosure of special category data. Further advice can be sought from the Information Commissioner.
See the Information Commissioner's Office website for the latest guidance and advice.