| Sigma Intelligence Limited | Information & communication | 2003 |
| Sigma One Holdings Limited | Financial services | 2017 |
| Sign Connections Limited | Professional & scientific | 1999 |
| Sign Force Limited | Manufacturing | 1997 |
| Signalong the Communication Charity | Wholesale & retail | 1994 |
| Signature Aesthetics Ltd | Health & social care | 2025 |
| Signature Barbers Ltd | Other services | 2024 |
| Signature Mobile Conversions Ltd | Professional & scientific | 2025 |
| Signature Moto Limited | Wholesale & retail | 2015 |
| Signpost Financial Holdings Limited | Financial services | 2014 |
| Signpost Mortgages Limited | Financial services | 2019 |
| Signs Express Group Limited | Financial services | 2017 |
| Signs Express Holdings Limited | Financial services | 2007 |
| Signs Express Limited | Manufacturing | 1989 |
| Silav Limited | Administrative & support | 2005 |
| Silenus Solutions Limited | Professional & scientific | 1993 |
| Silfield Homes Limited | Construction | 2021 |
| Silfield Self Storage Ltd | Transport & logistics | 2024 |
| Silicon Supplies Limited | Wholesale & retail | 2011 |
| Silk Chicken Ltd | Hospitality | 2012 |
| Silko Limited | Extraterritorial | 2015 |
| Sillitoe Solutions Limited | Professional & scientific | 2025 |
| Silly Smiles Limited | Health & social care | 2017 |
| Sillysouls Cafe & Bar Ltd | Hospitality | 2022 |
| Siltown Development Limited | Construction | 2024 |
| Silver Back Manufacturing Limited | Manufacturing | 2005 |
| Silver Bits Ltd | Information & communication | 2025 |
| Silver Cottage Ltd | Hospitality | 2020 |
| Silver Darlings (Lowestoft) Limited | Wholesale & retail | 2013 |
| Silver Ivory UK Ltd | Professional & scientific | 2020 |
| Silver LET Ltd | Real estate | 2019 |
| Silver Road PUB Company Ltd | Hospitality | 2025 |
| Silver Sound Limited | Arts & recreation | 2022 |
| Silver Stage Event Structures Limited | Administrative & support | 2011 |
| Silver-Dynamic Ltd | Wholesale & retail | 2024 |
| Silverain Management Ltd | Households | 2012 |
| Silverback Grooming Ltd | Extraterritorial | 2020 |
| Silverback Planning Solutions Ltd | Professional & scientific | 2024 |
| Silverback Scaffolding Ltd | Construction | 2017 |
| Silverhaven Developments Ltd | Construction | 2025 |
| Silverlink KA47 Limited | Hospitality | 2019 |
| Silvermoth Limited | Financial services | 2023 |
| Silvertap Limited | Real estate | 2002 |
| Silvi IT Ltd | Wholesale & retail | 2024 |
| Silvi Trading Ltd | Wholesale & retail | 2024 |
| Silvis Developments Ltd | Construction | 2020 |
| Silvis Investments Ltd | Financial services | 2020 |
| Sima Consultancy Limited | Professional & scientific | 2017 |
| Simax Norfolk Ltd | Wholesale & retail | 2022 |
| Simba Care Ltd | Health & social care | 2024 |
| Simba Securities Limited | Real estate | 1965 |
| Simbuck Design Ltd | Professional & scientific | 2016 |
| Simficity Limited | Information & communication | 2014 |
| Simflo Ltd | Transport & logistics | 2019 |
| Simma Black Ltd | Information & communication | 2021 |
| Simmonds Clockmaking Limited | Manufacturing | 2015 |
| Simmons Financial Referrals Ltd | Financial services | 2026 |
| Simms Farms Limited | Agriculture & fishing | 1957 |
| Simon Bailey and Partners Safeguarding Consultancy Ltd | Professional & scientific | 2021 |
| Simon Bowden Limited | Professional & scientific | 2010 |
| Simon Hall Communications Ltd | Professional & scientific | 1983 |
| Simon Pain Limited | Health & social care | 2010 |
| Simon Weir Ltd | Administrative & support | 2021 |
| Simon's Landscaping Limited | Professional & scientific | 2003 |
| Simona Summer Ltd | Wholesale & retail | 2026 |
| Simonds Decor Ltd | Construction | 2025 |
| Simontex Ltd | Health & social care | 2017 |
| Simothea Services Limited | Professional & scientific | 2025 |
| Simpco Commercial Ltd | Hospitality | 2008 |
| Simpco Retail Ltd | Hospitality | 2019 |
| Simper Law Limited | Professional & scientific | 2016 |
| Simper Property Developments Ltd | Real estate | 2020 |
| Simple Abodes Ltd | Real estate | 2026 |
| Simple Clothing Ltd | Wholesale & retail | 2025 |
| Simple Liquidation Limited | Financial services | 2019 |
| Simple Telecomms Ltd | Information & communication | 2015 |
| Simplee Delivered Ltd | Transport & logistics | 2024 |
| Simpler PR Limited | Professional & scientific | 2006 |
| Simpler Tax Ltd | Professional & scientific | 2024 |
| Simplicity Trading Limited | Wholesale & retail | 2004 |
| Simplifire Ltd | Construction | 2020 |
| Simply Ashes Limited | Manufacturing | 2024 |
| Simply Bread Limited | Manufacturing | 2021 |
| Simply Electric (Norfolk) Ltd | Construction | 2021 |
| Simply Marvellous Properties 3 Limited | Real estate | 2018 |
| Simply Psychology Ltd | Health & social care | 2014 |
| Simply Solutions Accountancy Services Ltd | Professional & scientific | 2020 |
| Simpson & Oliver (Property) Ltd | Real estate | 2023 |
| Simpson Marine Ltd | Professional & scientific | 2026 |
| Simrans Desserts Ltd | Hospitality | 2020 |
| Sims Bottega Ltd | Wholesale & retail | 2022 |
| Sims Images Limited | Professional & scientific | 2012 |
| Simstar Consultants Ltd | Extraterritorial | 2011 |
| Simyra Limited | Information & communication | 2020 |
| Sinclair International Limited | Manufacturing | 1991 |
| Sinclair Stainless Fabrications Limited | Manufacturing | 1970 |
| Sinclair Thomas Independent Financial Planning Ltd | Financial services | 2011 |
| Singer Holdings Ltd | Financial services | 2026 |
| Singhs Flakes Limited | Hospitality | 2019 |
| Singular Publishing Limited | Information & communication | 2015 |