Ahem:

After two and a half years in power, the Khmer Rouge was overthrown by the Vietnamese on Christmas Day, 1978. In the months and years that followed, the US and China and their allies, notably the Thatcher government, backed Pol Pot in exile in Thailand.

Although the Khmer Rouge government (“Democratic Kampuchea”) had ceased to exist in January 1979, its representatives were allowed to continue occupying Cambodia’s seat at the UN; indeed, the US, China and Britain insisted on it. Meanwhile, a Security Council embargo on Cambodia compounded the suffering of a traumatised nation, while the Khmer Rouge in exile got almost everything it wanted.

And it got worse from there….

https://www.newstatesman.com/politics/politics/2014/04/how-thatcher-gave-pol-pot-hand