https://www.gov.uk/check-uk-visa/y/hong-kong-(british-national-overseas)/tourism
What you need at the UK border
You must provide a valid passport or travel document. Your passport should be valid for the whole of your stay in the UK.
You may also be asked to prove that:
you’re visiting for tourism
you’re able to support yourself and your dependents during your trip (or have funding from someone else to support you)
you’ve arranged accommodation for your stay
you’re able to pay for your return or onward journey (or have funding from someone else)
you’ll leave the UK at the end of your visit
就咁睇,有錢,有親戚/朋友地址,如果有埋回程機票就應該問題不大了(不過可以留6個月,我都唔太sure係咪一定要回程機票)