| Simply Heating GAS Engineers Ltd | Construction | 2019 |
| Simply Inspect and Marine Ltd | Professional & scientific | 2024 |
| Simply Norwegian Limited | Other services | 2008 |
| Simply Rogue Ltd | Other services | 2019 |
| Simply Sales Solutions Ltd | Administrative & support | 2023 |
| Simplysmartsoftware Limited | Information & communication | 2016 |
| Simpson Agri-Plant Ltd | Wholesale & retail | 2023 |
| Simpson Orthodontics Limited | Health & social care | 2018 |
| Simpson Technical Solutions Ltd | Education | 2023 |
| Simsam News Limited | Wholesale & retail | 2002 |
| Simula Capital Limited | | 1996 |
| SIN Less Entertainment Ltd | Hospitality | 2023 |
| Sinclair Serviced Accommodation Ltd | Real estate | 2024 |
| Sindha Ltd | Wholesale & retail | 2024 |
| Sindhu Consultancy Limited | Professional & scientific | 2025 |
| Sinfinity Spaces Ltd | Households | 2024 |
| Singh Asian Directory Limited | Wholesale & retail | 2020 |
| Singh Property Mgmt Ltd | Real estate | 2019 |
| Singh's Newcastle Ltd | Wholesale & retail | 2021 |
| Singhpharm Ltd | Public administration | 2021 |
| Singing Light Music Limited | Information & communication | 2022 |
| Singisetti Srinivas Limited | Health & social care | 2014 |
| Singleton (Metal Works) Limited | Manufacturing | 2000 |
| Singleton Wind Ltd | Construction | 2026 |
| Singwithkaitlin Ltd | Education | 2025 |
| Sinha Pharma Ltd | Wholesale & retail | 2020 |
| Sinouk Academy of Science and Technology Limited | Information & communication | 2026 |
| Sintax Hospitality Ltd | Hospitality | 2022 |
| Sintons Limited Liability Partnership | | 2003 |
| Sintons Trust Corporation Limited | Extraterritorial | 2018 |
| SIP Symphony Coffee Limited | Hospitality | 2023 |
| Siplylife Ltd | Wholesale & retail | 2025 |
| SIR Bobby Robson Lounge Limited | Hospitality | 2026 |
| SIR John Fitzgerald (Holdings) Limited | Professional & scientific | 2009 |
| SIR John Fitzgerald,Limited | Wholesale & retail | 1926 |
| Siren Films Ltd. | Wholesale & retail | 2002 |
| Sirg Limited | Financial services | 2025 |
| Sirius Technologies Limited | Manufacturing | 2019 |
| Siriushair Ltd. | Other services | 2016 |
| Sirl Medicolegal Ltd | Professional & scientific | 2026 |
| Sirrah Properties Limited | Real estate | 2011 |
| SIS Decisions Ltd | Information & communication | 2023 |
| Sisbro One Limited | Real estate | 2015 |
| Sisi Stay Ltd | Real estate | 2025 |
| Sister ACT Holdings Limited | Administrative & support | 2019 |
| Sister ACT North East Limited | Health & social care | 2016 |
| Sister Shack CIC | Professional & scientific | 2019 |
| Sister Sounds Ltd | Information & communication | 2022 |
| Sisters of Grace Ltd | Wholesale & retail | 2020 |
| Sisters With Sparkle NE Ltd | Administrative & support | 2025 |
| Site and Field Engineering Ltd | Professional & scientific | 2019 |
| Site-Lab Ltd | Professional & scientific | 2013 |
| Sitebuilder Internet Limited | Information & communication | 2003 |
| Sitebuilder Limited | Information & communication | 2003 |
| Sivani Limited | Wholesale & retail | 2026 |
| Sivee (UK) Ltd. | Information & communication | 2023 |
| SIX Circles Limited | Administrative & support | 2017 |
| SIX Marias Ltd | Wholesale & retail | 2024 |
| SIX Northern Properties Limited | Real estate | 2022 |
| SIX SIX Digital Marketing Limited | Professional & scientific | 2023 |
| SIX Ventures Group Limited | Financial services | 2026 |
| Sixty-Two Stanhope Gardens Limited | Households | 1993 |
| Siyanda Investment Ltd | Administrative & support | 2025 |
| Sizzle (NE) Ltd | Hospitality | 2023 |
| Sizzlenspice Limited | Transport & logistics | 2025 |
| Sizzling Pepperoni Ltd | Hospitality | 2024 |
| SJ & SJ Properties Limited | Real estate | 2018 |
| SJ Developments Northern Ltd | Construction | 2017 |
| SJ Investments & Finance Limited | Administrative & support | 2022 |
| SJ Manufacturing & Installations Ltd | Manufacturing | 2016 |
| SJ Manufacturing Ltd | Professional & scientific | 2026 |
| SJ Mason Estates Limited | Other services | 2018 |
| SJ Topco Limited | Professional & scientific | 2023 |
| SJ Virtual Business Solutions Limited | Administrative & support | 2024 |
| SJ Virtual Business Support Limited | Administrative & support | 2023 |
| SJD Fabrication Ltd | Manufacturing | 2019 |
| SJH Tail Lift Services Limited | Wholesale & retail | 2012 |
| SJL Joinery Limited | Construction | 2017 |
| SJP Roofing Services Ltd | Construction | 2021 |
| SJR Motors Ltd | Wholesale & retail | 2025 |
| SJR19 Recruitment Ltd | Transport & logistics | 2024 |
| SJS Group Enterprises Ltd | Hospitality | 2024 |
| SJS Hospitality Group Ltd | Hospitality | 2025 |
| SJS Property Investments Ltd | Real estate | 2020 |
| SJS Solutions Ltd | Information & communication | 2001 |
| SK BD Kitchen Ltd | Hospitality | 2023 |
| SK Building Services Limited | Construction | 2003 |
| SK Ecotraders Ltd | Wholesale & retail | 2025 |
| SK GAS Heating and Plumbing Limited | Construction | 2024 |
| SK Motors N.E Limited | Wholesale & retail | 2024 |
| SK Prestige Realty Limited | Real estate | 2026 |
| SK Rail & Civils Limited | Administrative & support | 2023 |
| SK Sourcing Ltd | Administrative & support | 2026 |
| SK1 Properties Ltd | Real estate | 2020 |
| SKA Investments Ltd | Administrative & support | 2016 |
| Skaters Club Limited | Arts & recreation | 2007 |
| Skavn UK Ltd | Wholesale & retail | 2025 |
| SKD Electrical Solutions Ltd | Construction | 2020 |
| Skedaddle Cycle Hub Limited | Wholesale & retail | 2012 |
| Skedaddle Limited | Administrative & support | 1999 |