National insurance contribution for employment overseas

Hi there, I had moved to UK from Hong Kong 3 years ago. I maintained the employment with my employer in Hong Kong and work remotely in UK. As my employer does not have any business in UK, I did tax return by Self Assessment and income tax had been paid. However, I was not informed for contribution of any class of National Insurance. Could you advise whether I should have National Insurance contribution? If I need, what kind of National Insurance contribution should I do and what is the procedure to apply? Thank you very much for your advice.

Hi,
You will need to write to HMRC to request a liability decision regarding the payment of National Insurance contributions. Please provide the following information in your letter:
•    full name
•    National Insurance Number
•    date of birth
•    date you left the UK - if applicable
•    your most recent UK address
•    your address abroad – if applicable
•    the type of work you do
•    your company name and address – UK and abroad
•    where your contract is held
•    how often you work in the UK
•    your normal working pattern (the days, weeks or months you regularly work)
The address to write to is:
PT Operations North East England
International Caseworker Department
HM Revenue and Customs,
BX9 1AN
They will provide you with a written response to your queries.
Thank you.