Hi
As a non UK resident, you can choose to send your tax return online by buying a commercial tax return ,alist of commercial suppliers can be found at
Self Assessment commercial software suppliers section and submitting it by 31 January each year or you can download a paper SA100 (tax return) SA109 (residence) and any other supplementary pages which can be found at
Self Assessment tax return forms Please note that the entire tax return should be submitted in the same format, eg. either online in its entirity or on paper.