In Good medical practice, we say the following:
41.‘You must be honest and objective when writing references, and when appraising or assessing the performance of colleagues, including locums and students. References must include all information relevant to your colleagues’ competence, performance and conduct.’
71. ‘You must be honest and trustworthy when writing reports, and when completing or signing forms, reports and other documents. You must make sure that any documents that you write or sign are not false or misleading.
a. You must take reasonable steps to check the information is correct.
b. You must not deliberately leave out relevant information.’
In Leadership and management for all doctors we also say the following:
34. ‘You must be honest and objective and keep to the principles of equality and diversity when appraising or assessing colleagues’ performance. This includes when assessing trainees during the Annual Review of Competence Progression (ARCP) or other equivalent process. The safety of patients and the public could be put at risk if you make false, exaggerated or incomplete comments about another professional’s competence or experience.’
This explanatory guidance provides more detail about how to follow these principles. It also explains to candidates what they can expect to be included in any references written about them.
Serious or persistent failures to follow this supplementary guidance will put your registration at risk.
Prospective employers use references to gather information about a candidate’s qualifications and employment history and to help them assess their suitability for the post in question.1 They also give both employers and candidates an opportunity to verify the information supplied in an application. So you should write references in a way that is fair to both the candidate2 and the prospective employer.
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).
Employers need to be confident that they can rely on the information in references, particularly when they are employing healthcare professionals. Candidates also need to be confident that references written about them are accurate and reliable. A reference that presents an inaccurate picture of a prospective employee could lead either to an unsuitable candidate being appointed or the most suitable person not being appointed. In some cases this will put patients at risk of serious harm and it may undermine trust in the profession.
You must be honest and fair when providing references. You should usually provide a reference if you are the person best placed to do so. When providing a reference, you should state the basis upon which you are making your assessment of the candidate, such as how long you have known them and in what capacity.
When assessing whether information is relevant, you should consider whether including it (or leaving it out) could mislead an employer3 about either a specific issue or the overall suitability of a candidate. If you agree to provide a reference, you must do the following:
- Only provide comments that you can substantiate.
- Provide comments that are objective, fair and unambiguous.
- Do not base comments on your personal views4 about a candidate that have no bearing on the candidate’s suitability.
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.
You should include all information you are aware of that is relevant to a candidate’s professional competence and be prepared to provide evidence to support this, where appropriate.
You should provide information about a candidate’s conduct, including matters that might affect a patient’s trust in the individual candidate or the public’s trust in the profession as a whole.
You should draw attention to any other issues that could put patients at risk. This may include information relating to unresolved, outstanding or past complaints about the candidate’s competence, performance or conduct, if you judge that this is relevant to the candidate’s suitability. You should take reasonable steps to check the information you provide. If this is not practical, or the information is incomplete, you should make this clear.
You should not usually include personal information about a candidate, for example in relation to their health, in a reference. However, a situation may arise where you are aware of confidential information about a candidate that has a direct bearing on their suitability for the particular post in question. In these circumstances, you should get consent to disclose the information. If this is not practical or appropriate, or consent is withheld, you should consider whether the benefits (to individual patients or the public) of disclosing the information would outweigh the possible harm to the individual candidate. For example, including health information may be justified if it is necessary to protect patients from risk of serious harm.5 You can find more guidance on releasing information in the public interest in paragraphs 63 - 70 of Confidentiality.6
Confidential medical care is recognised in law as being in the public interest. The fact that people are encouraged to seek advice and treatment benefits society as a whole as well as the individual. But there can be a public interest in disclosing information to protect individuals or society from risks of serious harm, such as from serious communicable diseases or serious crime.23
If it is not practicable or appropriate to seek consent, and in exceptional cases where a patient has refused consent, disclosing personal information may be justified in the public interest if failure to do so may expose others to a risk of death or serious harm. The benefits to an individual or to society of the disclosure must outweigh both the patient’s and the public interest in keeping the information confidential.
Such a situation might arise, for example, if a disclosure would be likely to be necessary for the prevention, detection or prosecution of serious crime, especially crimes against the person. When victims of violence refuse police assistance, disclosure may still be justified if others remain at risk, for example from someone who is prepared to use weapons, or from domestic violence when children or others may be at risk.
Other examples of situations in which failure to disclose information may expose others to a risk of death or serious harm include when a patient is not fit to drive,24 or has been diagnosed with a serious communicable disease,25 or poses a serious risk to others through being unfit for work.26
When deciding whether the public interest in disclosing information outweighs the patient’s and the public interest in keeping the information confidential, you must consider:
- the potential harm or distress to the patient arising from the disclosure – for example, in terms of their future engagement with treatment and their overall health
- the potential harm to trust in doctors generally – for example, if it is widely perceived that doctors will readily disclose information about patients without consent
- the potential harm to others (whether to a specific person or people, or to the public more broadly) if the information is not disclosed
- the potential benefits to an individual or to society arising from the release of the information
- the nature of the information to be disclosed, and any views expressed by the patient
- whether the harms can be avoided or benefits gained without breaching the patient’s privacy or, if not, what is the minimum intrusion.
If you consider that failure to disclose the information would leave individuals or society exposed to a risk so serious that it outweighs the patient’s and the public interest in maintaining confidentiality, you should disclose relevant information promptly to an appropriate person or authority.
If you consider that failure to disclose the information would leave individuals or society exposed to a risk so serious that it outweighs the patient’s and the public interest in maintaining confidentiality, you should disclose relevant information promptly to an appropriate person or authority. You should inform the patient before disclosing the information, if it is practicable and safe to do so, even if you intend to disclose without their consent.
Decisions about whether or not disclosure without consent can be justified in the public interest can be complex. Where practicable, you should seek advice from a Caldicott or data guardian or similar expert adviser who is not directly connected with the use for which disclosure is being considered. If possible, you should do this without revealing the identity of the patient.
You must document in the patient’s record your reasons for disclosing information with or without consent. You must also document any steps you have taken to seek the patient’s consent, to inform them about the disclosure, or your reasons for not doing so.
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.
If a candidate asks for a copy of the reference, you should usually give them a copy, though you are not required to do so.7