Non-resident withholding tax on interest

I reside in and am a tax resident of Singapore. I currently receive interest payments from a UK investment company paid net of any withholding tax, which currently applies at 20% for all individuals and for companies and other entities based outside the UK. Given the UK and Singapore double taxation treaty, I believe I am eligible to receive interest paid gross of withholding tax. Is this understanding correct? If so, how may I apply to HMRC to provide the relevant documents justifying my eligibility to receive interest payments gross to the UK investment company? Thank you

Hi,
Please refer to Tax on your UK income if you live abroad
Thank you.