Hi Alice Russell,
There are no Income Tax implications on the receipt of a cash gift unless the cash gift generates interest or dividends.
These would then potentially be subject to tax.
Further guidance can be found here:
Tax on savings interest
Tax on dividends
Any gift would only from part of your estate if from the UK.
You may however want to check with the tax authorities in Hong Kong to see if it is taken into account there.
Thank you.