| SI Specialist Services Ltd | Health & social care | 2024 |
| SI Tea Stall Limited | Hospitality | 2023 |
| SIA Shafer Limited | Real estate | 2016 |
| Siac Systems Ltd | Information & communication | 2010 |
| Sial Beauty and Textile Ltd | Wholesale & retail | 2023 |
| Sibbi Global Ltd | Wholesale & retail | 2025 |
| Sibbs Care Ltd | Health & social care | 2020 |
| Siblings Property Investments Ltd | Real estate | 2024 |
| Sibtl Ltd | Real estate | 2018 |
| SIC Transit Ltd | Professional & scientific | 2022 |
| Sicocreative Ltd | Professional & scientific | 2017 |
| SID 212 Solutions Limited | Wholesale & retail | 2025 |
| SID Investments Ltd | Real estate | 2020 |
| Sidat Consulting Ltd | Professional & scientific | 2026 |
| Side by Side Space CIC | Education | 2025 |
| Side Grip Piling Limited | Construction | 2009 |
| Sidfam Investments Ltd | Real estate | 2024 |
| Sieblertec Ltd | Information & communication | 2021 |
| Sienna Retail Ltd | Hospitality | 2025 |
| Sierra Bravo Digital Limited | Professional & scientific | 2025 |
| Sierra Leone Advocacy Movement- Global (Slam-Global) Ltd | Professional & scientific | 2024 |
| Sieufttrading Ltd | Wholesale & retail | 2026 |
| Sieve Consultancy Ltd | Professional & scientific | 2024 |
| Siew Property Investment Ltd | Real estate | 2026 |
| Siezac Limited | Professional & scientific | 2022 |
| SIF Ahmad Limited | Health & social care | 2016 |
| Sifeh Ltd | Wholesale & retail | 2022 |
| Sightworks Limited | Health & social care | 2024 |
| Sigma Couriers Ltd | Transport & logistics | 2025 |
| Sigma Credit Hire Ltd | Administrative & support | 2025 |
| Sigma Leathers Limited | Wholesale & retail | 2025 |
| Sigma Projects (Control Panels) Limited | Manufacturing | 2013 |
| Sigma Tech Solutions Ltd | Information & communication | 2023 |
| Sign Factory Ltd | Manufacturing | 2017 |
| Sign Hub Limited | Wholesale & retail | 2021 |
| Sign Masters NW Limited | Construction | 2019 |
| Signage Print Identity Limited | Construction | 2023 |
| Signalsphere Ltd | Information & communication | 2024 |
| Signature Chromes Limited | Manufacturing | 2025 |
| Signature Dental Laboratory Limited | Health & social care | 2021 |
| Signature Developments (Manchester) Limited | Construction | 2005 |
| Signature Digital Dental Laboratory Limited | Manufacturing | 2019 |
| Signature Dog Grooming Limited | Professional & scientific | 2021 |
| Signature Electrical Limited | Construction | 2018 |
| Signature Estates Bolton Ltd | Real estate | 2025 |
| Signature Finish Landscapes Ltd | Administrative & support | 2025 |
| Signature Investments (NW) Ltd | Real estate | 2023 |
| Signature King Ltd | Wholesale & retail | 2025 |
| Signature Living (Manchester) Limited | Construction | 2008 |
| Signature Logistics Ltd | Wholesale & retail | 2020 |
| Signature Planning Services Ltd | Professional & scientific | 2015 |
| Signature Property Investment Limited | Hospitality | 2012 |
| Signature Smiles Ltd. | Health & social care | 2021 |
| Signature Trade Frames Ltd | Construction | 2025 |
| Signific Digital Ltd | Wholesale & retail | 2022 |
| Signs & Graphics Bolton Limited | Professional & scientific | 2019 |
| Signs Services Ltd | Manufacturing | 2001 |
| Signtech Visual Solutions Ltd | Manufacturing | 2017 |
| Sikari Solutions Limited | Information & communication | 2024 |
| Silcocks Property Services Ltd | Real estate | 2024 |
| Silent Breeze Ltd | Wholesale & retail | 2025 |
| Silentwaltz Ltd | Wholesale & retail | 2019 |
| Siliconmg Limited | Real estate | 2023 |
| Silk Avenue Limited | Wholesale & retail | 2013 |
| Silk Chauffeur Ltd | Administrative & support | 2023 |
| Silk Executive Travel Ltd | Administrative & support | 2021 |
| Silk JET Ltd | Wholesale & retail | 2023 |
| Silk Solicitors Limited | Professional & scientific | 2011 |
| Silk Travel Ltd | Administrative & support | 2026 |
| Silkroadauctions Ltd | Wholesale & retail | 2026 |
| Silky Skin Limited | Other services | 2022 |
| Silli Store Ltd | Wholesale & retail | 2025 |
| Silmet Ltd | Transport & logistics | 2021 |
| Silous Holt Holdings Ltd | Administrative & support | 2022 |
| Silteq Limited | Manufacturing | 1971 |
| Silva Hardwood Flooring Limited | Manufacturing | 2000 |
| Silva Trading Limited | Transport & logistics | 2018 |
| Silver Birch Joinery Ltd | Construction | 2025 |
| Silver City Consultancy Limited | Professional & scientific | 2019 |
| Silver Music Entertainment Limited | Information & communication | 2020 |
| Silver Street Bar Co Ltd | Hospitality | 2024 |
| Silver Wren Ltd | Administrative & support | 2024 |
| Silverback Labs Ltd | Wholesale & retail | 2022 |
| Silverbirch Services Ltd | Transport & logistics | 2024 |
| Silverburn Finance (U.K.) Limited | Financial services | 1962 |
| Silverburn Trading Company Limited | Agriculture & fishing | 1932 |
| Silvergate Housing Limited | Real estate | 2026 |
| Silverglide (Holdings) Limited | Administrative & support | 2022 |
| Silverglide Ltd | Construction | 2007 |
| Silverline Medical Limited | Health & social care | 2005 |
| Silverline Motor Company NW Ltd | Wholesale & retail | 2017 |
| Silverline Property Ltd | Real estate | 2019 |
| Silvermont House Ltd | Wholesale & retail | 2026 |
| Silverstone Creative Ltd | Other services | 2024 |
| Silverstone Solutions Ltd | Wholesale & retail | 2025 |
| Silverwood Forestry Limited | Agriculture & fishing | 1991 |
| Silviculture Solutions Limited | Agriculture & fishing | 2024 |
| SIM Bala Camera Ltd | Information & communication | 2016 |
| SIM Free Ltd | Wholesale & retail | 2012 |
| Simbar Limited | Professional & scientific | 2015 |