| Shuttersup Ltd | Construction | 2010 |
| SI Assets Limited | Real estate | 2020 |
| SI Electrical Limited | Construction | 1997 |
| SI Travel Ltd | Administrative & support | 2022 |
| SI Units Ltd | Professional & scientific | 2015 |
| SIA Services Limited | Real estate | 2013 |
| Sibs Salon (Blackfen) Limited | Other services | 2013 |
| Sicl Art Limited | Arts & recreation | 2018 |
| Sidcup 07 Limited | Real estate | 2025 |
| Sidcup Auto Repairs Limited | Manufacturing | 2013 |
| Sidcup Barbers Limited | Other services | 2022 |
| Sidcup Beauty Studios Ltd | Other services | 2022 |
| Sidcup Data Limited | Information & communication | 2025 |
| Sidcup Day Nursery Ltd | Education | 2021 |
| Sidcup Dental Spa Ltd | Health & social care | 2026 |
| Sidcup DRY Cleaning Limited | Other services | 2022 |
| Sidcup Engineering Limited | | 1958 |
| Sidcup Interiors Ltd | Administrative & support | 2016 |
| Sidcup Matters Ltd | Other services | 2025 |
| Sidcup Partners Ltd | Administrative & support | 2016 |
| Sidcup Propties Limited | Real estate | 2018 |
| Sidcup Rugby Football Club Limited | Arts & recreation | 2011 |
| Sidcup Spice Ltd | Hospitality | 2024 |
| Sidneyrail Limited | Construction | 2016 |
| Siena JAY Beauty Limited | Other services | 2026 |
| Sigeng Ltd | Construction | 2017 |
| Signal Motors Limited | Wholesale & retail | 2024 |
| SIGNAL42 Ltd | Information & communication | 2025 |
| Signpost Signs Limited | Administrative & support | 2004 |
| Signscription Ltd | Administrative & support | 2023 |
| Silam Ltd | Hospitality | 2023 |
| Silva Lining Solutions Ltd | Manufacturing | 2014 |
| Silver ASH Properties Limited | Real estate | 2017 |
| Silver FOX Rentals Limited | Real estate | 2021 |
| Silver Spoon Development Limited | Real estate | 2021 |
| Silver Spring Graphics Limited | Professional & scientific | 2011 |
| Silversteel Scaffolding Ltd | Wholesale & retail | 2004 |
| Simel Limited | Administrative & support | 2011 |
| Simon Kemp Online Jewellers Limited | Administrative & support | 2016 |
| Simon Webster Electrical Limited | Construction | 2024 |
| Simplify ANY Space Ltd | Other services | 2026 |
| Simplistic Training Solutions Limited | Education | 2017 |
| Simply Authentic Ltd | Hospitality | 2010 |
| Simpson Roofing Services Ltd | Administrative & support | 2024 |
| Simpsons Plumbing Services Ltd | Construction | 2019 |
| Singhesri Limited | Hospitality | 2025 |
| Siriestates Ltd | Real estate | 2017 |
| Sirihealthcare Ltd | Health & social care | 2018 |
| Sisi Softplay Ltd | Administrative & support | 2026 |
| Site Labour UK Ltd | Administrative & support | 2018 |
| Sitec ESP Limited | Administrative & support | 2018 |
| Sizzlerize Digital Limited | Information & communication | 2022 |
| SJ Bar 97 Ltd | Hospitality | 2025 |
| SJ Chicken Ltd | Hospitality | 2021 |
| SJ Health Ltd | Administrative & support | 2023 |
| SJA Technical Services Limited | Construction | 2018 |
| SJC Training Academy of Hair and Beauty T/A HB Academy Ltd | Education | 2018 |
| SJM Construction Services Limited | Construction | 2003 |
| Sjreece Consulting Ltd | Information & communication | 2023 |
| Sjsupplies Limited | Construction | 2015 |
| SK Elevator Services Ltd | Professional & scientific | 2023 |
| SK33 Ltd | Hospitality | 2023 |
| Skala Homes UK Ltd | Real estate | 2021 |
| Skape Media Ltd | Professional & scientific | 2022 |
| Skate Electrical Limited | Construction | 2015 |
| Skin Avenue London Ltd | Other services | 2025 |
| Skin Matters by Colette Ltd | Health & social care | 2024 |
| Skin Science Aesthetics Ltd | Professional & scientific | 2022 |
| Skin Sentry Ltd | Manufacturing | 2022 |
| SKS Consultancy Limited | Professional & scientific | 2017 |
| Sktk Developments Limited | Construction | 2020 |
| Skyla Rose Accounting Services Ltd | Professional & scientific | 2025 |
| Skylog Services Ltd | Construction | 2021 |
| Skyward Access Training Limited | Other services | 2007 |
| Skyward Training Limited | Administrative & support | 2015 |
| SL Property Solutions Limited | Professional & scientific | 2016 |
| Slabtrack Limited | Professional & scientific | 2021 |
| Slatter's Investments Limited | Real estate | 1965 |
| SLB Management Limited | Construction | 2010 |
| Sleep Clinic (2021) Limited | Health & social care | 2021 |
| Slim Mediation Ltd | Professional & scientific | 2015 |
| SLP Electrical Service London Ltd | Construction | 2021 |
| SLS Abode Ltd | Real estate | 2026 |
| SLS Management Solutions Limited | Financial services | 2011 |
| Slugger Action London Limited | Administrative & support | 2014 |
| SM Commissioning Ltd | Administrative & support | 2020 |
| Smart Brands UK Holdings Limited | Wholesale & retail | 1995 |
| Smart Fibre Optic Solution Ltd | Information & communication | 2021 |
| Smart Heating GAS & Plumbing Limited | Other services | 2015 |
| Smart Teenies Ltd | Other services | 2007 |
| Smart-Move Property Services Ltd | Real estate | 2024 |
| Smartroots Learners Hubs Ltd | Education | 2026 |
| Smartspec Education Ltd | Information & communication | 2025 |
| Smashnbun UK Limited | Hospitality | 2025 |
| SMB Facades Ltd | Construction | 2022 |
| SMD Heating & Maintenance Ltd | Construction | 2019 |
| SMD Residential Ltd | Real estate | 2022 |
| SMH Commercial Management Limited | Professional & scientific | 2024 |
| SMH Commercial Solutions Limited | Professional & scientific | 2020 |
| SMH Ventures Ltd | Hospitality | 2026 |