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No, you don't need a Chinese visa to visit Hong Kong SAR, under the One country - two systems principle. China and Hong Kong SAR have separate visa/immigration policies and requirements.
From the UK's foreign travel advice page for Hong Kong:
Although Hong Kong is now part of the Peopleβs Republic of China it remains a Special Administrative Region with its own immigration controls. You can visit Hong Kong for up to 6 months without a visa.
You do not need a Chinese visa unless you plan to also visit mainland China.