| Simple Methods Limited | Extraterritorial | 2014 |
| Simple Parking Ltd | Hospitality | 2025 |
| Simpletin Consulting Ltd | Information & communication | 2016 |
| Simplico Ltd | Wholesale & retail | 2026 |
| Simplified Global Limited | Professional & scientific | 2025 |
| Simplu SI Atat Limited | Construction | 2025 |
| Simply Deez Events CIC | Wholesale & retail | 2020 |
| Simply Indigo Solutions Limited | Information & communication | 2026 |
| Simply Lets PK Ltd | Real estate | 2020 |
| Simply Move Estate and Lettings Management Ltd | Real estate | 2016 |
| Simply Pharm Ltd | Health & social care | 2016 |
| Simply Recycling Luton Limited | Water & waste | 2014 |
| Simply Sparkling Ltd | Administrative & support | 2025 |
| Simply Thai Ltd | Hospitality | 2016 |
| Simply Ventures Limited | Real estate | 2025 |
| Simply Water Ltd | Water & waste | 2016 |
| Simply Wedding Cakes Ltd | Manufacturing | 2022 |
| Simran Dessert Limited | Hospitality | 2025 |
| Sims Inter Co Limited | Transport & logistics | 2018 |
| Simsport Ltd | Wholesale & retail | 2025 |
| SIN Fast Trans Ltd | Transport & logistics | 2026 |
| Sinachi Group of Company Ltd | Health & social care | 2019 |
| Sindhtech Limited | Information & communication | 2013 |
| Sinfonia Verdi Limited | Arts & recreation | 1996 |
| Singh Civil Ltd | Construction | 2023 |
| Singh Gardening Ltd | Administrative & support | 2025 |
| Singh Houses Ltd | Real estate | 2024 |
| Singh RJ Transport Limited | Transport & logistics | 2023 |
| Singh’S Unique Builder Limited | Construction | 2025 |
| Singusta Transport Ltd | Transport & logistics | 2016 |
| Sino Associates Business Consultancy Limited | Other services | 2015 |
| Sintha Properties Ltd | Real estate | 2018 |
| Sinthu Private Limited | Wholesale & retail | 2025 |
| Sinthusha Private Limited | Wholesale & retail | 2025 |
| Sinus Limited | Construction | 2012 |
| Sinx Ltd | Wholesale & retail | 2026 |
| Siphar Ltd | Information & communication | 2011 |
| Sips Specialists Limited | Construction | 2017 |
| SIQ Limited | Professional & scientific | 2015 |
| SIR Syed Investments Limited | Real estate | 2021 |
| Sirenidae Ltd | Transport & logistics | 2019 |
| Siri Tech Services Ltd | Information & communication | 2020 |
| Sirihomes Ltd | Hospitality | 2023 |
| Sirloin Steak Ltd | | 2016 |
| SIS Office Interiors Limited | Wholesale & retail | 2011 |
| SIS Recovery & Breakdown 24/7 Ltd | Wholesale & retail | 2022 |
| Sister Action Ltd | Other services | 2023 |
| Sisterhood Store Limited | Wholesale & retail | 2019 |
| Sistermatic Change CIC | Health & social care | 2025 |
| Sisto Brands Limited | Wholesale & retail | 2019 |
| Sita Capital Partners LLP | | 2016 |
| Site Engineering Supply Ltd | Construction | 2008 |
| Site FIX Sollution Ltd | Construction | 2017 |
| Site Labour Services Limited | Construction | 2014 |
| Site Subby Limited | Professional & scientific | 2024 |
| Sito.Ai Ltd | Information & communication | 2024 |
| Sivinei & Mircelangelo Ltd | Construction | 2018 |
| Sivko Limited | Real estate | 2020 |
| SIX Capitals Ltd | Financial services | 2017 |
| SIX Sigma Consultancy Ltd | Wholesale & retail | 2020 |
| Sixhills Consulting Limited | Professional & scientific | 2001 |
| Sixonetwo Limited | Wholesale & retail | 2005 |
| Size YOU Ltd | Manufacturing | 2022 |
| Sizzle Ltd | Hospitality | 2025 |
| Sizzle N Flame Ltd | Hospitality | 2024 |
| Sizzle Van Limited | Wholesale & retail | 2026 |
| Sizzling Fusion Ltd | Hospitality | 2024 |
| SJ City Ltd | Wholesale & retail | 2022 |
| SJ Driveways & Landscapes Ltd | Administrative & support | 2018 |
| SJ Luton Limited | Financial services | 2020 |
| SJ Males & Co Limited | Other services | 2009 |
| SJ Motor Group Ltd | Wholesale & retail | 2022 |
| SJ Security Ltd | Administrative & support | 2025 |
| SJ Stores Luton Ltd | Wholesale & retail | 2026 |
| SJ Tiffin Box Limited | Hospitality | 2025 |
| SJ Tredarz Ltd | Wholesale & retail | 2017 |
| Sj&I Holdings Ltd | Financial services | 2025 |
| SJB Unique Services Ltd | Professional & scientific | 2026 |
| Sjivan Limited | Wholesale & retail | 2024 |
| SK & SK Ltd | Real estate | 2022 |
| SK Builders Ltd | Construction | 2021 |
| SK Capital Ventures Ltd | Wholesale & retail | 2020 |
| SK Dosanjh Ltd | Manufacturing | 2024 |
| SK Electrical and GAS Services Limited | Professional & scientific | 2013 |
| SK Entrepreneurs Ltd | Wholesale & retail | 2025 |
| SK Finance Consultants Ltd | Professional & scientific | 2021 |
| SK Foods Store Limited | Wholesale & retail | 2015 |
| SK Hitchin Limited | Hospitality | 2020 |
| SK Investments (Luton) Ltd | Real estate | 2015 |
| SK IP Holdings Ltd | Financial services | 2026 |
| SK Lettings & Management Services Limited | Real estate | 2020 |
| SK Luton Services Ltd | Transport & logistics | 2024 |
| SK Motoring Group Limited | Wholesale & retail | 2016 |
| SK Poultry & Meat Limited | Wholesale & retail | 2021 |
| SK Properties LTN Ltd | Real estate | 2023 |
| SK Property Luton Ltd | Real estate | 2026 |
| SK Salons Ltd. | Other services | 2017 |
| SK Solutions Group Ltd | Professional & scientific | 2024 |
| SK Western Europe Limited | Information & communication | 2012 |
| SK Wholesale Luton Ltd | Wholesale & retail | 2020 |