| Sirghi Transport Limited | Transport & logistics | 2019 |
| Siriluck Limited | Professional & scientific | 2015 |
| SIS Properties Service Ltd | Real estate | 2022 |
| Siskin Marketing Ltd | Information & communication | 2015 |
| Sisters Four Consortium Limited | Construction | 2017 |
| Site Grid Energy Limited | Construction | 2025 |
| Site Managerment Ltd | Administrative & support | 2015 |
| Site Plant Services Hire Limited | Administrative & support | 1983 |
| Site Safety Academy Limited | Education | 2025 |
| Site Safety Systems Limited | Information & communication | 2016 |
| Site Track Pro Ltd | Construction | 2020 |
| Site-Care Limited | Construction | 2019 |
| Sitecrete Limited | Manufacturing | 2022 |
| Siththa Ltd | Wholesale & retail | 2023 |
| Sitota Limited | Education | 2022 |
| Situal Cave Ltd | Arts & recreation | 2021 |
| Situnario Limited | Professional & scientific | 2015 |
| Sivilov Ltd | Transport & logistics | 2019 |
| SIX & Eight Homes Ltd | Real estate | 2023 |
| SIX Degree Management Limited | Construction | 2024 |
| SIX Sigma Group Limited | Professional & scientific | 2002 |
| SIX Star Alliance Ltd | Information & communication | 2016 |
| SIX TEN Media Ltd | Other services | 2011 |
| SIX00FOUR Ltd | Information & communication | 2017 |
| Sixfields Autocentre (Midlands) Limited | Wholesale & retail | 2017 |
| Sixfields Cars Ltd | Wholesale & retail | 2024 |
| Sixfields Recovery Limited | Transport & logistics | 2025 |
| Sixteen Homes Build Ltd | Real estate | 2018 |
| Sixteen Homes Ltd | Real estate | 2020 |
| Sixth Degree Construction Ltd | Construction | 2024 |
| Sixth Voice Productions Limited | Professional & scientific | 2014 |
| Sixty & SIX Limited | Professional & scientific | 2015 |
| Siyana Ltd | Hospitality | 2022 |
| Sizesutra Ltd | Information & communication | 2024 |
| Sizzle Shack N Shots Ltd | Hospitality | 2024 |
| Sizzle Station Ltd | Hospitality | 2026 |
| Sizzling LAB Ltd | Hospitality | 2025 |
| SJ & Co Build Ltd | Construction | 2020 |
| SJ Cafe Ltd | Hospitality | 2023 |
| SJ Coaching & Advisory Limited | Professional & scientific | 2021 |
| SJ Construction Northampton Ltd | Construction | 2024 |
| SJ Doody Ltd | Transport & logistics | 2018 |
| SJ Fire Safety Consultants Ltd | Professional & scientific | 2026 |
| SJ Smart Engineering Ltd | Manufacturing | 2015 |
| SJ Surveying (Corby) Limited | Professional & scientific | 2022 |
| SJ Taxi Limited | Transport & logistics | 2025 |
| SJB Plumbing & Heating Limited | Construction | 2024 |
| SJH Sporthorses Ltd | Wholesale & retail | 2025 |
| SJJ Legal Ltd | Professional & scientific | 2025 |
| SJM Rentals & Properties Ltd | Real estate | 2020 |
| Sjmp Diagnostic & Surgical Ltd | Health & social care | 2019 |
| Sjmr Limited | Other services | 2011 |
| SJP Associates Limited | Real estate | 2022 |
| SJR (CW) Ltd | Hospitality | 2025 |
| SJS Builderz Ltd | Construction | 2024 |
| SJS Childcare Limited | Education | 2015 |
| SJS Flat Roofing Limited | Construction | 2025 |
| SJS Flore Ltd | Hospitality | 2023 |
| SJS Hub Ltd | Administrative & support | 2018 |
| SJS Superstore Limited | Wholesale & retail | 2025 |
| SJW Northampton Limited | Financial services | 2024 |
| SK Automotive Ltd | Wholesale & retail | 2025 |
| SK Beauty & Wellness Ltd | Wholesale & retail | 2018 |
| SK Consulting Group Ltd | Information & communication | 2019 |
| SK Distribution & Wholesale (UK) Ltd | Wholesale & retail | 2009 |
| SK Employment Law Limited | Professional & scientific | 2016 |
| SK Fixing Ltd | Construction | 2015 |
| SK Sehmi Consulting Limited | Professional & scientific | 2014 |
| SK20 Limited | Health & social care | 2020 |
| SK20 Properties Ltd | Real estate | 2021 |
| SK58 Ltd | Transport & logistics | 2023 |
| SK701 Ltd | Arts & recreation | 2017 |
| SKA Investments & Legal Consult Ltd | Construction | 2025 |
| Skanda Info Ltd | Information & communication | 2022 |
| Skate Hub Ltd | Arts & recreation | 2025 |
| SKB Accountancy Ltd | Professional & scientific | 2026 |
| Sketchbox Concepts Ltd | Professional & scientific | 2015 |
| Sketchley Estimating Services Ltd | Construction | 2024 |
| Sketchproposal Ltd | Professional & scientific | 2019 |
| Skevos Projects Ltd | Construction | 2026 |
| SKH Global Limited | Transport & logistics | 2024 |
| Skiddaw Haulage Ltd | Transport & logistics | 2025 |
| Skiers Lodge Guide Service Limited | Health & social care | 2004 |
| Skill-Serve Training Limited | Education | 2009 |
| Skillbright Ltd | Professional & scientific | 2014 |
| Skilled UP C.I.C. | Professional & scientific | 2018 |
| Skin Care Secrets Ltd | Wholesale & retail | 2024 |
| Skin Deep Medispa Ltd | Other services | 2019 |
| Skin Retreat Limited | Other services | 2012 |
| Skin Solutions by Bella Limited | Other services | 2024 |
| Skin Spa Embassy Ltd | Other services | 2024 |
| Skinflint Limited | Administrative & support | 2002 |
| Skinluxe Group Limited | Administrative & support | 1998 |
| Skinner Commercials Ltd | Wholesale & retail | 2021 |
| Skinny Builders Limited | Construction | 2024 |
| Skins Vinyl and Wrapping Limited | Manufacturing | 2022 |
| Skinwear Limited | Manufacturing | 2008 |
| Skipat 79 Transport Ltd | Transport & logistics | 2022 |
| Skippsense Limited | Professional & scientific | 2023 |
| Skips on Wheels Ltd | Transport & logistics | 2024 |