BBC Editorial Guidelines §3.2.2: "All BBC output...must be well sourced, based on sound evidence, thoroughly tested"

Quote (BBC Editorial Guidelines §3.2.2):

"All BBC output, as appropriate to its subject and nature, must be well sourced, based on sound evidence, thoroughly tested and presented in clear, precise language."

Source: https://www.bbc.co.uk/editorialguidelines/guidelines/accuracy (2019 edition).

Confidence: Verified.

Companion §3.3.4 (single-source reluctance):

"We should be reluctant to rely on a single source. If we do rely on a single source, it should be credible, and a named, on-the-record source is always preferable."

Companion §3.2.3 (attribution required when uncorroborated):

"Claims, allegations, material facts and other content that cannot be corroborated should normally be attributed."

For Candid use: The BBC §3 cluster is the cleanest single editorial-standards source. Three rules, all transferable to marketing content: (1) sound evidence basis, (2) prefer named on-the-record sources to single anonymous sources, (3) attribute the uncorroborated. Pairs with Reuters Handbook of Journalism: "A named source is always preferable to an unnamed source. Anonymous sources are the weakest sources" and SPJ Code of Ethics (2014): "Identify sources clearly. The public is entitled to as much information as possible to judge reliability and motivations".