The British Consulate-General in Hong Kong is not authorised to perform marriages ceremonies. Marriages in Hong Kong performed in accordance with Hong Kong law are generally recognised in UK law. Unlike marrying in Mainland China, Hong Kong does not require a Certificate of No Impediment (CNI), a document which shows there are no objections to your marriage.
Once a British National is married, he can also deposit his Marriage Certificate with the General Records Office (GRO) in the UK but it is not a requirement in UK law.
According to current Hong Kong law, a marriage may not be contracted if either party is under the age of 16. Intending marrying party over 16 but not yet reaching 21 will require the parent/custodian's written consent.
Please note that in UK law, a foreign national does not automatically acquire British nationality through marriage to a British national. If you marry a Hong Kong national, they will require a visa to visit or settle in the UK. English language ability requirements may also apply. Detailed information on how to apply for a visa or settlement can be obtained from the UK Borders Agency.