| Seachill UK Limited | Manufacturing | 1950 |
| SEB Decorating Limited | Construction | 2023 |
| Secmatics Limited | Information & communication | 2018 |
| Second Child Ltd | Information & communication | 2016 |
| Secure and Recruit Limited | Administrative & support | 2018 |
| Secure Home Electrics Ltd | Construction | 2017 |
| Secure View Windows & Doors Ltd | Construction | 2026 |
| Security Management Resources Limited | Administrative & support | 2007 |
| SEL Cleaning Services Ltd | Administrative & support | 2017 |
| Select Tours and Cruises Limited | Extraterritorial | 2015 |
| Select Travel Service (North) Ltd | Professional & scientific | 1998 |
| Select Travel Service Limited | Other services | 1994 |
| Semimed Ltd | Professional & scientific | 2023 |
| Sendmattersuk Ltd | Education | 2022 |
| September Breeze Limited | Extraterritorial | 2014 |
| Seraphic Bookkeeping Solutions Ltd | Professional & scientific | 2022 |
| Serious About ST Neots Ltd | Information & communication | 2023 |
| Serjeants at Law Limited | Administrative & support | 2017 |
| Service Lettings Limited | Households | 2025 |
| Servowarm Limited | Construction | 2016 |
| Sesome Limited | Administrative & support | 2019 |
| Setsquare Property Limited | Real estate | 2021 |
| SFC Peterborough Ltd | Hospitality | 2018 |
| Sflt (Group) Ltd | Administrative & support | 2023 |
| SFS Electrical Contractors Limited | Construction | 2020 |
| SFS Property (ST Ives) Limited | Real estate | 2023 |
| SGM Motorsport Limited | Wholesale & retail | 2024 |
| SGP Digital Solutions Ltd | Information & communication | 2025 |
| SGR (Cambs) Ltd | Construction | 2018 |
| SGR Electronics Ltd | Manufacturing | 2010 |
| Shadies Limited | Administrative & support | 2016 |
| Shai Digital Ltd | Information & communication | 2026 |
| Sharp Branding Ltd | Wholesale & retail | 2015 |
| Sharp Property Care Ltd | Households | 2023 |
| Shaun Mccarthy Consult Limited | Professional & scientific | 2026 |
| Shears Polar Limited | Professional & scientific | 2017 |
| Shelford Road Developments Ltd | Construction | 2022 |
| Shelley Thermoformers International Limited | Manufacturing | 1956 |
| Shelton Estates Limited | Agriculture & fishing | 1949 |
| Shepreth Development Ltd | Real estate | 2011 |
| Sheriffs Carpets Ltd | Wholesale & retail | 2005 |
| Sherlyn Store's Ltd | Wholesale & retail | 2026 |
| Sherwood Architects Limited | Professional & scientific | 2011 |
| Shook Technical Services Limited | Manufacturing | 2026 |
| Shorts Circuits Ltd | Construction | 2023 |
| Show Floors LLP | | 2012 |
| Show-Sound Productions Limited | Arts & recreation | 2024 |
| SHP Scientific Ltd | Manufacturing | 2016 |
| Shred & Recycle Limited | Water & waste | 2006 |
| Shuudda Cuudda Wuudda Limited | Transport & logistics | 2015 |
| Side Mission Travel Limited | Administrative & support | 2025 |
| Sidewinderuk.Com Ltd | Administrative & support | 2010 |
| Sidney C. Banks (Farms) Limited | Real estate | 1951 |
| Sierra Aircraft Training and Maintenance Ltd. | Other services | 2013 |
| Sikles Limited | Real estate | 2025 |
| Silhouette Kimbolton Limited | Other services | 2014 |
| Silicon Bay Limited | Information & communication | 1996 |
| Silicon Consultants Limited | Information & communication | 1993 |
| Silva-Trans Ltd | Transport & logistics | 2014 |
| Silver Fern Agri Ltd | Agriculture & fishing | 2023 |
| Silver Lantern Publishing Ltd | Information & communication | 2025 |
| Silver Secrets Limited | Extraterritorial | 2016 |
| Silverbirch Electronics Limited | Wholesale & retail | 2017 |
| Silverwood Construction (Cambridge) Ltd | Construction | 2009 |
| Simba Ventures Limited | Transport & logistics | 2021 |
| Simily Holdings Ltd | Real estate | 2024 |
| Simon Green Motorsport Ltd | Wholesale & retail | 2018 |
| Simon Laws Ltd | Transport & logistics | 2025 |
| Simplifi Limited | Professional & scientific | 2025 |
| Simul Excellentia Limited | Professional & scientific | 2025 |
| Simulator Training Solutions Ltd | Information & communication | 2024 |
| Sineidin O'Reilly Therapy Services Ltd | Health & social care | 2022 |
| Sington & Co Limited | Information & communication | 2004 |
| Sirron Composites Limited | Administrative & support | 2024 |
| Sisco Architecture Limited | Professional & scientific | 2008 |
| Sisco Forensic Engineers Limited | Professional & scientific | 2006 |
| Sisimia Transport Ltd | Transport & logistics | 2020 |
| Sisters' Beauty Lounge Ltd | Other services | 2025 |
| Site Survey Solutions Ltd | Construction | 2019 |
| Site Syndications Limited | Construction | 2003 |
| Siteset Business Support Ltd | Administrative & support | 2022 |
| Sizzle Shack Limited | Hospitality | 2023 |
| SJJ Fast Food Ltd | Hospitality | 2026 |
| SK Platinum Limited | Other services | 2015 |
| Skerry Electrical Ltd | Construction | 1959 |
| Skilful Strategies Limited | Education | 2016 |
| Sky Kingdom Ltd | Real estate | 2024 |
| Skylark Psychology Ltd | Education | 2025 |
| Skyroute Haulage Ltd | Transport & logistics | 2025 |
| SLB Wholesale Ltd | Wholesale & retail | 2016 |
| Slingshot Therapeutics Holdings Limited | Financial services | 2024 |
| Slingshot Therapeutics Limited | Financial services | 2024 |
| SLM Accountants Ltd | Professional & scientific | 2018 |
| SLY Industries Ltd | Real estate | 2025 |
| Smallwood Computer Services Limited | Information & communication | 1998 |
| Smart ABC Cambs Limited | Wholesale & retail | 2026 |
| Smart Cars Private Hire Ltd | Transport & logistics | 2020 |
| Smart Solutions of Peterborough Limited | Wholesale & retail | 2006 |
| Smart Stay Accommodation Ltd | Hospitality | 2023 |
| Smart Worxs Automotive Ltd | Manufacturing | 2025 |