Hi Chris Wong,
Article 18 of the UK / Hong Kong tax treaty advises that salaries, wages and other similiar remunerations paid by the Government of Hong Kong, shall be taxable only in Hong Kong.
UK/HONG KONG DOUBLE TAXATION AGREEMENT AND PROTOCOL
This means that your civil service employment and civil service pension are not taxable in the UK.
They will continue to be taxable in Hong Kong, even when you are resident in the UK.
You would only show them in the free hand notes box of the tax return, so that you are declaring the pension in the interest of full disclosure.
Thank you.