Facebook has removed more than 130 accounts, pages and groups it says were part of a UK-based misinformation network.
The company said it was the first time it had taken down a UK-based group targeting messages at British citizens.
The same group set up pages posing both as far-right outlets and anti-fascist activists.
Facebook said it had shared its discovery with law enforcement and the government.
The group was able to gain followers by setting up innocent-looking pages and groups. It later renamed them, and started posting politically-motivated content.
MP Damian Collins, who chairs a committee investigating fake news, said it was the "tip of the iceberg".
Facebook said about 175,000 people followed at least one of the fake pages, which included 35 profiles on Instagram.
The company said the pages "engaged in hate speech and spread divisive comments on both sides of the political debate in the UK".
"They frequently posted about local and political news including topics like immigration, free speech, racism, LGBT issues, far-right politics, issues between India and Pakistan, and religious beliefs including Islam and Christianity.
"We're taking down these pages and accounts based on their behaviour, not the content they posted. In each of these cases, the people behind this activity coordinated with one another and used fake accounts to misrepresent themselves, and that was the basis for our action."
The BBC understands Facebook discovered the network of inauthentic accounts while investigating hate speech about the UK Home Secretary Sajid Javid.
Facebook said the pages had spent about $1,500 (£1,140) on advertising between them. The earliest advert was placed in December 2013, and the most recent in October 2018.
Facebook said it had not completed its "review of the organic content coming from these accounts".
Separately, the company has also removed 31 pages, groups and accounts for engaging in "co-ordinated inauthentic behaviour" in Romania.
These accounts, not linked to the UK network, posted biased news in support of the Social Democratic Party.