| Signature Carpets and Flooring Limited | Construction | 2015 |
| Signature Consulting Direct Ltd | Wholesale & retail | 2026 |
| Signature Dental Ceramics Limited | Health & social care | 2012 |
| Signature Energy Limited | Energy | 2022 |
| Signature GAS and Power Limited | Energy | 2026 |
| Signature Kitchens Installations Ltd | Construction | 2026 |
| Signature Motorcycles Ltd | Wholesale & retail | 2018 |
| Signature Residential Limited | Real estate | 2024 |
| Signature Ribbon Company Limited | Extraterritorial | 2001 |
| Signature SKI Limited | Administrative & support | 2007 |
| Signet Resources Limited | Administrative & support | 2003 |
| Signetum Ltd | Professional & scientific | 2015 |
| Signifer Limited | Professional & scientific | 2018 |
| Signsx Ltd | Construction | 2025 |
| SIH Consultancy Limited | Professional & scientific | 2024 |
| Sija Development Limited | Construction | 2025 |
| Sikaa Limited | Wholesale & retail | 2016 |
| Sikandari & Co. Ltd | Health & social care | 2021 |
| Sikander & Sons Properties Ltd | Real estate | 2025 |
| Sikham Limited | Hospitality | 2023 |
| Sikmij LAT Limited | Information & communication | 2025 |
| Silama Ltd | Administrative & support | 2025 |
| Silas Tutors Limited | Education | 2025 |
| Silcocks Estates Limited | Real estate | 1946 |
| Silehurst Tech Limited | Information & communication | 2025 |
| Silene Ventures Limited | Wholesale & retail | 2024 |
| Siliro Ltd | Real estate | 2024 |
| Silk Flowers UK Limited | Wholesale & retail | 2019 |
| Silk Projects Ltd | Real estate | 2020 |
| Silkoak Ltd | Real estate | 2020 |
| Sillah & Sons Ltd | Health & social care | 2019 |
| Sillah Planning Ltd | Professional & scientific | 2026 |
| Sillars Consulting Ltd | Professional & scientific | 2024 |
| Silly Point Ltd | Wholesale & retail | 2025 |
| Silo Systems Ltd. | Professional & scientific | 2006 |
| Silou Active Ltd | Wholesale & retail | 2015 |
| Silou Holdings Limited | Financial services | 2021 |
| Siltech Limited | Manufacturing | 2006 |
| Silurian Studios Limited | Information & communication | 2025 |
| Silva Building Ltd | Construction | 2024 |
| Silvadore LLP | | 2023 |
| Silver Analytics Limited | Professional & scientific | 2021 |
| Silver Birch Stables Limited | Construction | 2019 |
| Silver Lining Flue Services Limited | Administrative & support | 2023 |
| Silver Marlin Fish Bar Limited | Hospitality | 2019 |
| Silver Recruitment Agencies Limited | Administrative & support | 2025 |
| Silver Silas Ltd | Information & communication | 2026 |
| Silver Solutions Limited | Information & communication | 2025 |
| Silver Voices Limited | Other services | 2020 |
| Silverback Gyms Limited | Health & social care | 2024 |
| Silverback Surveillance Limited | Administrative & support | 2020 |
| Silverbirch Construction Ltd | Construction | 2017 |
| Silverbirch Housing Ltd | Real estate | 2019 |
| Silverbirch Properties & Investments Limited | Real estate | 2020 |
| Silverbug Limited | Information & communication | 2002 |
| Silverdale Tours (Nottingham) Limited | Transport & logistics | 1977 |
| Silverhawk Developments Ltd | Real estate | 2024 |
| Silverledge Partners Ltd | Professional & scientific | 2025 |
| Silverlock Training Limited | Professional & scientific | 2009 |
| Silvermesh UK Limited | Real estate | 2026 |
| Silverrock Healthcare Ltd | Health & social care | 2025 |
| Silverstone Property Services Ltd | Construction | 2023 |
| Silverstripe Management Services Ltd | Professional & scientific | 2020 |
| Silverwood Crafts Limited | Manufacturing | 2022 |
| Silvina Limited | Professional & scientific | 2022 |
| SIM Engineering Ltd | Construction | 2024 |
| Sim&Co Property Investments Ltd | Real estate | 2023 |
| Simaluda Limited | Financial services | 2020 |
| Simands Hospitality Ltd | Hospitality | 2011 |
| Simba & Frans Ltd | Construction | 2020 |
| Simba Locum Limited | Health & social care | 2023 |
| Simba Luxe Traders Ltd | Wholesale & retail | 2025 |
| Simbafrans Limited | Wholesale & retail | 2023 |
| Simbec Solutions Ltd | Professional & scientific | 2010 |
| Simbha Burgers & Wraps Ltd | Hospitality | 2025 |
| Simbrix Limited | Manufacturing | 2014 |
| Simco Real Estate Services Limited | Professional & scientific | 2020 |
| Simdeb Limited | Professional & scientific | 2016 |
| Simetty Ltd | Administrative & support | 2012 |
| Simex Group Ltd | Wholesale & retail | 2022 |
| Simian Distribution Limited | Wholesale & retail | 2014 |
| Simity Ltd | Information & communication | 2023 |
| Simkins Farm Management Company Ltd | Real estate | 2010 |
| Simla Delight Ltd | Hospitality | 2025 |
| Simla Fine Dining Ltd | Hospitality | 2024 |
| Simla Indian Kimberley Ltd | Hospitality | 2026 |
| Simlar 2 Limited | Wholesale & retail | 2000 |
| Simlpe Limited | Public administration | 2026 |
| Simms Coaching and Consultancy Ltd | Education | 2022 |
| Simms Investment Properties Limited | Real estate | 2022 |
| Simms Land Services Limited | Other services | 2024 |
| Simon Cadby Consulting Ltd | Information & communication | 2013 |
| Simon Clayson Design Limited | Information & communication | 2008 |
| Simon Cooke IT Contracting Limited | Administrative & support | 2018 |
| Simon Dovell Innovations Limited | Other services | 2013 |
| Simon Flear Consulting Limited | Financial services | 2015 |
| Simon Frost Associates Limited | Financial services | 2004 |
| Simon GEE Designs Limited | Professional & scientific | 2014 |
| Simon JP Taylor Enterprises Limited | Information & communication | 2023 |
| Simon Nicholas Associates Ltd | Administrative & support | 2009 |