K Y Wong

Hello, I am seeking advice on which part of tax return should I fill in (foreign/self-employment). I am working as a individual consultant (non company) for a Hong Kong Organisation (non-resident company, not under Construction Industry Scheme) under a contractor contract get paid monthly without any employee benefit which fits the terms of 'Foreign' part said 'INCOME FROM A NON RESIDENT COMPANY'. Also, I would like to voluntarily pay class 2 National Insurance. 1) Should I consider myself as a self-employment in this cases? 2) Is there any different of the term 'subcontractor' and 'contractor'? How should I defined myself in these? Thanks!