An "official spokesman" is someone who is authorized to speak on behalf of an organization, government, or authority. They provide information and represent the organization's views or positions to the public and media. Full definition
The prime minister's official spokesman said a referendum in this parliament remained «an option» but insisted there was no urgency to resolve the issue. (news.bbc.co.uk)
«This is not a straightforward black and white issue,» the prime minister's official spokesman told reporters this morning. (politics.co.uk)
The prime minister's official spokesman acknowledged that the wording of the texts had changed since the campaign began. (bbc.co.uk)