Thanks for your response. Yes, I've already established with your help from previous question that this should be income tax - that's not my question.
I'm completing the tax return myself. I'd like to know.. on the tax return form (http://www.hmrc.gov.uk/forms/sa100.pdf), where do put the forex income (under which section)?
I was thinking maybe is falls under the section 2 - self employment. Supplementary form for this section is at http://search2.hmrc.gov.uk/kb5/hmrc/forms/view.page?record=HgZl_CADaKU&formId=3182. However, this asks for business description and business postcode. Given that I'm not registered as a business, I'm not sure if this is the correct section.
Please let me know if I can further clarify my question.
Thank you Rakhi