“ These templates are intended to be used in a nested fashion, with a line-feed between the template invocation and any content, including the template calls within a section for a sub-section and then paragraphs that are nested.
No formatting is applied by default.
Formatting for at each level can be applied through CSS by targetting the .__ukpga_l1,.__ukpga_l2,.__ukpga_l2,.__ukpga_l4 selectors in conjunction with the .__ukpga__cl_act_p_number (paragraph numbering) and .__ukpga__cl_act_p_number_inner (character style for the number) . ”

“ In published editions, these are typically the 'bold' numbered portions of the text. In older published editions a section may have a "side title" for the section in the margin, this should be included as the title parameter. ”

“ UK primary legislation consists of nested content being in increasing depth (sections, subsections, "paragraphs", ) ( See w:Citation_of_United_Kingdom_legislation#Citation_of_specific_provisions_within_an_Act_or_other_instrument)
The templates are:
{{ukpga/l1}} - Opens a level 1 "Section". The l1 parameter is used to provide the number of the section, and any punctuation for this should be remove. The content generated by this template will include an anchor of the form l1.0 (e.g 1.0, 2.0, 3.0, etc.) so as to not conflict the anchors used for Page: links. ”