Hi yick,
As you were employed by the Hong Kong government, your employment income is not taxable in the UK, unless you are a UK national and you were working for the Hong Kong government while resident in the UK.
If your employment income is only taxable in Hong Kong, you do not need to declare in the UK. You can see article 18 of the UK/Hong Kong double taxation agreement here:
2010 Hong Kong-UK DTA
Thank you.