| Simanda Living Limited | Real estate | 2012 |
| Simba Clothing Ltd | Wholesale & retail | 2026 |
| Simon Elis Landscaping Ltd | Administrative & support | 2013 |
| Simonabuild Ltd | Construction | 2022 |
| Simonian Medical Limited | Health & social care | 2014 |
| Simple Advice Limited | Administrative & support | 2013 |
| Simple Maids Ltd | Administrative & support | 2025 |
| Simple Mortgages Limited | Financial services | 2019 |
| Simplicity Fashion Limited | Wholesale & retail | 2025 |
| Simply Clean (Chichester) Ltd | Administrative & support | 2019 |
| Simply Facials Limited | Other services | 2025 |
| Simply the Best Bar Limited | Hospitality | 2025 |
| Simrena Limited | Real estate | 2017 |
| Sims Builders Limited | Extraterritorial | 1982 |
| SIN Homes Ltd | Professional & scientific | 2021 |
| SIN House Ltd | Real estate | 2021 |
| Singh City Limited | Construction | 2022 |
| Single PLY Solutions Ltd | Construction | 2013 |
| Siosic Property Services Ltd | Real estate | 2022 |
| SIP and Solve Ltd | Arts & recreation | 2025 |
| Sirius Analysis Group Limited | Financial services | 2025 |
| Sirron Assets Limited | Real estate | 2004 |
| Sistemec Limited | Education | 2023 |
| Site AID Services Ltd | Administrative & support | 2021 |
| Site Spray Solutions Ltd | Construction | 2024 |
| Sivas Trading (GB) Ltd | Wholesale & retail | 2013 |
| SIX Pack Chick Limited | Information & communication | 2011 |
| Sixank Limited | Real estate | 2024 |
| Sixten & Cassey Limited | Real estate | 1921 |
| Sizzleandcofamily Ltd | Hospitality | 2026 |
| Sizzlin' Shenanigans Ltd | Administrative & support | 2025 |
| SJC Interiors Limited | Construction | 2019 |
| SJC Marketing Group Ltd | Professional & scientific | 2025 |
| SJD Auto Salvage Ltd | Wholesale & retail | 2022 |
| SJD Trading Ltd | Wholesale & retail | 2021 |
| SJH Contracting Ltd | Construction | 2024 |
| SJH Property Maintenance Ltd | Administrative & support | 2017 |
| SJK Management Services Limited | Wholesale & retail | 2025 |
| Sjmp Property Ltd | Construction | 2019 |
| SJP Consultants Limited | Professional & scientific | 2022 |
| SJS Social Care Limited | Health & social care | 2016 |
| SK ENT Ltd | Wholesale & retail | 2023 |
| SK FRY Limited | Hospitality | 2015 |
| Skadeens Errand Limited | Other services | 2015 |
| SKB Lettings Ltd | Real estate | 2016 |
| SKC Enterprises Ltd | Hospitality | 2025 |
| Skelliga Ltd | Professional & scientific | 2018 |
| SKI Collection Ltd | Administrative & support | 2005 |
| Skillvia Academy Limited | Education | 2020 |
| Skinner Skates Ltd | Arts & recreation | 2019 |
| Skinner’S Home Maintenance Ltd | Administrative & support | 2022 |
| Skinny Earnings Ltd | Arts & recreation | 2025 |
| Skinportant Limited | Other services | 2023 |
| SKL Property Leasing Ltd | Real estate | 2021 |
| SKR IT Consulting Limited | Information & communication | 2019 |
| Skribe Ltd | Professional & scientific | 2007 |
| Skubalt Ltd | Construction | 2022 |
| Sky Crane Services Limited | Construction | 2017 |
| Sky High Wealth Ltd | Real estate | 2021 |
| Skydom Limited | Health & social care | 2023 |
| Skye Installations(Southern) Limited | Administrative & support | 2023 |
| Skyline Engineering Solutions Ltd | Construction | 2024 |
| Skyline Event Services Ltd | Administrative & support | 2021 |
| Skyline Properties South Limited | Construction | 2014 |
| Skyline Roofing Limited | Construction | 2016 |
| Skyline Technical Services Limited | Professional & scientific | 2025 |
| Skypurple Cloud Limited | Information & communication | 2017 |
| Skysphere Industries Ltd | Public administration | 2025 |
| SL Consultancy & Training Ltd | Information & communication | 2020 |
| SL Developments (Portsmouth) Ltd | Construction | 2015 |
| SL Ports Limited | Hospitality | 2016 |
| SL Properties Southern Limited | Real estate | 2013 |
| SL Services & Logistics Ltd | Transport & logistics | 2025 |
| SLA Quantity Surveying Ltd | Professional & scientific | 2015 |
| Slantforge Ltd | Manufacturing | 2024 |
| Sldceilings&Interiors Ltd | Construction | 2021 |
| Sledgehammer Solutions Limited | Manufacturing | 1998 |
| Sleep Studio (Portsmouth) Limited | Real estate | 2024 |
| Sleep Studio Limited | Wholesale & retail | 2020 |
| Sleepright Direct Limited | Real estate | 2009 |
| SLG Southern Ltd | Construction | 2010 |
| SLG Waste Management Ltd | Water & waste | 2021 |
| SLH Eventing Limited | Arts & recreation | 2023 |
| Slim Butcher Limited | Wholesale & retail | 2023 |
| SLIMBUTCHER1 Limited | Wholesale & retail | 2026 |
| Slippery Sucker Ltd | Hospitality | 2020 |
| SLL Estates Limited | Households | 2017 |
| SLM Recycling Limited | Administrative & support | 2016 |
| Slowtide Limited | Wholesale & retail | 2017 |
| Small Island Catering Ltd | Hospitality | 2016 |
| Small World Car Hire Ltd | Administrative & support | 2024 |
| Smallbones Roofing Limited | Construction | 2020 |
| Smallbrook Properties Limited | Real estate | 2025 |
| Smart & Stylish Co-Living Limited | Real estate | 2022 |
| Smart Access Southern Ltd | Construction | 2022 |
| Smart Emergency Technologies Limited | Manufacturing | 2025 |
| Smart Roofer Ltd | Construction | 2021 |
| Smart-Fit Training Limited | Arts & recreation | 2013 |
| Smartcare Appliances Limited | Other services | 2026 |
| Smartest Ltd | Other services | 2008 |