Hi,
If the statutory residence test confirms that you are not UK tax resident for the whole tax year, you only declare your UK income for the whole tax year and your worldwide income, from the date you arrived in the UK.
Article 11 of the tax treay applies to interest and states 'may be' taxed in that other party. That phrase allows both countries to tax the interest. You would claim a credit in Hong Kong for any tax deducted against your UK interest.
Hong Kong: tax treaties
Thank you.