| Sillandental Limited | Health & social care | 2025 |
| Silva Ridge Ltd | Agriculture & fishing | 2026 |
| Silvarious Holdings Limited | Financial services | 2024 |
| Silvarious Limited | Wholesale & retail | 2008 |
| Silver (Eco) Ltd | Agriculture & fishing | 2021 |
| Silver Beauty Furniture Ltd | Wholesale & retail | 2019 |
| Silver Birch Creative Limited | Arts & recreation | 2008 |
| Silver Birch Financial Services Ltd | Financial services | 2018 |
| Silver Birch Psychotherapy Ltd | Health & social care | 2024 |
| Silver Green Logistics Ltd | Transport & logistics | 2025 |
| Silver Oak Logistics Limited | Transport & logistics | 2025 |
| Silver Peacock Events Limited | Other services | 2014 |
| Silver Willows Residents Management Company Limited | Households | 2025 |
| Silver Xpress Limited | Construction | 2020 |
| Silverboxit Ltd | Information & communication | 2015 |
| Silvergate Group Ltd | Construction | 2025 |
| Silverhat Limited | Administrative & support | 2016 |
| Silverhill Housing CIC | Real estate | 2019 |
| Silverhill Impact Limited | Professional & scientific | 2024 |
| Silverhill Properties (Derby) Limited | Real estate | 2023 |
| Silverhill Support Ltd | Health & social care | 2019 |
| Silverhill UK Fish Bar Ltd | Hospitality | 2025 |
| Silverpoint Group Ltd | Information & communication | 2025 |
| Silverseal (GB) Ltd | Construction | 2009 |
| Sima Business Consultancy Limited | Professional & scientific | 2022 |
| Simar Transport Limited | Transport & logistics | 2023 |
| Simba Leisure UK Limited | Arts & recreation | 2019 |
| Simian NDT Limited | Professional & scientific | 2026 |
| Simms Land Investments Limited | Real estate | 2025 |
| Simoco Emea Ltd | Information & communication | 2002 |
| Simoco Limited | Information & communication | 1982 |
| Simoco Wireless Solutions Limited | Information & communication | 2009 |
| Simon Dakin Limited | Financial services | 2007 |
| Simon Foote Architects Limited | Professional & scientific | 2007 |
| Simon Frith Electrical Limited | Construction | 2014 |
| Simon Hartle Developments Limited | Construction | 2017 |
| Simon Hudson Consulting Limited | Professional & scientific | 2016 |
| Simon Padgett & Co Ltd | Professional & scientific | 2014 |
| Simon Pickering Limited | Real estate | 2010 |
| Simon Smith Online Ltd | Other services | 2019 |
| Simon Wareing Carpentry Ltd | Manufacturing | 2022 |
| Simon Wolsey Limited | Financial services | 2024 |
| Simone Greenfield Limited | Other services | 2019 |
| Simpatica Group Holdings Limited | Financial services | 2021 |
| Simpatica Group Limited | Financial services | 2017 |
| Simple PCP Claims Ltd | Information & communication | 2025 |
| Simple Property Group Ltd | Construction | 2023 |
| Simple Property Holdings Ltd | Financial services | 2025 |
| Simpletvsolutions Ltd | Construction | 2020 |
| Simplicib Ltd | Hospitality | 2020 |
| Simplicity Apartments Ltd | Hospitality | 2019 |
| Simplify Ltd | Professional & scientific | 2010 |
| Simplify Management Services Limited | Administrative & support | 2017 |
| Simplify Umbrella Resources Ltd | Administrative & support | 2017 |
| Simplify Umbrella Technical Limited | Administrative & support | 2017 |
| Simply Branded Ltd | Manufacturing | 2023 |
| Simply Driven Exec Cars Limited | Transport & logistics | 2026 |
| Simply Driven Executive Cars Ltd | Transport & logistics | 2020 |
| Simply Fibre Limited | Construction | 2018 |
| Simply Inspired Fitness One Ltd | Other services | 2020 |
| Simply Reflexology Ltd | Administrative & support | 2011 |
| Simply Secured Network Limited | Financial services | 2022 |
| Simply SET UP Ltd | Professional & scientific | 2022 |
| Simply Smocking Ltd | Wholesale & retail | 2023 |
| Simply Uniform Limited | Wholesale & retail | 2015 |
| Simpouser Ltd | Professional & scientific | 2024 |
| Simpson Jones Limited Liability Partnership | | 2010 |
| Simpson Kitchens Ltd | Manufacturing | 2009 |
| Simpson MCS Limited | Professional & scientific | 2025 |
| Simpson Performance Ltd | Arts & recreation | 2026 |
| Simpson's Property Ltd | Real estate | 2023 |
| Simptech Solutions Ltd | Construction | 2022 |
| Simran Consultancy Ltd | Administrative & support | 2025 |
| Simranjeet Chahal Ltd | Transport & logistics | 2025 |
| Simrit Holdings Ltd | Real estate | 2025 |
| Sims Financial Services Limited | Financial services | 2016 |
| Simulation (Ters) Limited | Extraterritorial | 1999 |
| Simulation International Limited | Extraterritorial | 2000 |
| Sina Healthcare Ltd | Health & social care | 2021 |
| Sinalearn Ltd | Education | 2025 |
| Sinam Enterprises Ltd | Administrative & support | 2025 |
| Sinfin Campervans Ltd | Wholesale & retail | 2025 |
| Sinfin Community Centre Ltd. | Arts & recreation | 2003 |
| Sinfin Community Childcare | Education | 2002 |
| Sinfin Fish Bar Ltd | Hospitality | 2019 |
| Sinfin Test Centre Limited | Wholesale & retail | 2022 |
| Singh Auto Imports Ltd | Wholesale & retail | 2025 |
| Singh Gill Ltd | Hospitality | 2025 |
| Singh Mortgages Limited | Financial services | 2023 |
| Singh Property Group Ltd | Real estate | 2025 |
| Singh Speed Ltd | Wholesale & retail | 2023 |
| Sinoboom UK Ltd | Wholesale & retail | 2024 |
| SIR John Port's Charity | Education | 2002 |
| Siren Consultancy Limited | Financial services | 2023 |
| Sirius a* Properties Ltd | Households | 2024 |
| Siskin Homes Limited | Construction | 2016 |
| Siskin Spaces Ltd | Real estate | 2024 |
| Sissco Ltd | Wholesale & retail | 2008 |
| Sista Spice LP | | 2013 |
| Sister Rock Ltd | Hospitality | 2024 |