Hi,
From my understanding of your question, you re-mortgaged your primary residence in Hong Kong in order to purchase a buy-to-let property in the UK, with your question relating to the mortgage linked to this property.
If the money raised through the re-mortgage has been used towards a mortgage on the UK property then you would be correct in that mortgage interest may be claimed at the basic rate.
If, however the interest relates to the property in Hong Kong then this would not be claimable as the expense was not incurred wholly and exclusively for the rental property business as it relates to your personal residence:
please see:
PIM2054
PIM2058
PIM2054
PIM2058
Thank you.