| Sustenergia Ltd | Construction | 2025 |
| Suzen Financial Solutions Limited | Professional & scientific | 2021 |
| SVN Projects Ltd | Administrative & support | 2024 |
| SVP Associates Limited | Professional & scientific | 2004 |
| SW4U Limited | Arts & recreation | 2024 |
| Swagat Harpenden Ltd | Hospitality | 2026 |
| Swanne Boutique Ltd | Wholesale & retail | 2024 |
| Sweet Honeydew Limited | Information & communication | 2021 |
| Sweu Limited | Professional & scientific | 2014 |
| Swingcroft Limited | Agriculture & fishing | 1976 |
| Swoosh Digital Limited | Information & communication | 2006 |
| SWS Consulting Ltd | Professional & scientific | 2025 |
| Syber-Tec Consulting Ltd | Information & communication | 2019 |
| Synapsys Investment Company Limited | Real estate | 2001 |
| Syncfore Technology Solutions Ltd | Information & communication | 2019 |
| Synergia Corporate Solutions Limited | Administrative & support | 2024 |
| Synergy Group London Ltd | Professional & scientific | 2026 |
| T Dennehy Limited | Construction | 2019 |
| T&J Capital Ltd | Administrative & support | 2013 |
| T. K. O. Daniel Dubois Limited | Arts & recreation | 2017 |
| T.K.O Caroline Dubois Ltd | Arts & recreation | 2019 |
| T.Meredith Roberts and Company Limited | Financial services | 1933 |
| T4S Associates Ltd | Administrative & support | 2024 |
| Tabacon Management Limited | Real estate | 2002 |
| Tabacon NFC LLP | | 2014 |
| Tabacon Stansted 2 Limited | Real estate | 2007 |
| Tailored Maintenance & Home Improvements Limited | Construction | 2014 |
| Talbury Assessing Limited | Administrative & support | 2025 |
| Talisse Limited | Other services | 2012 |
| Talkeasy Communications Limited | Information & communication | 1998 |
| Talow Consultancy Ltd | Administrative & support | 2025 |
| Talverne Consulting Limited | Administrative & support | 2012 |
| Tamer Koseli Ltd | Wholesale & retail | 2021 |
| Tanglewood (Harpenden) Limited | Real estate | 1984 |
| Taragan Limited | Education | 2020 |
| Tattersall Holding Limited | Real estate | 2017 |
| Tawe Ltd | Real estate | 2022 |
| Tax Advice 1ST Limited | Professional & scientific | 2024 |
| Taxassist Accountants (B&H) Limited | Professional & scientific | 2005 |
| TAY TAR Thai (Harpenden) Ltd | Hospitality | 2021 |
| TEAM17 Football Coaching Ltd | Education | 2025 |
| Tecfutures Ltd | Professional & scientific | 2022 |
| Tech Events AI Ltd | Information & communication | 2024 |
| Technology Management Consulting Ltd | Professional & scientific | 2024 |
| Tedi Ltd | Administrative & support | 2015 |
| Tema Construction Ltd | Construction | 2019 |
| Tempest Capital Investments Limited | Financial services | 2023 |
| TEN Fifty-Six Limited | Administrative & support | 2017 |
| TEN to Nine Ltd | Hospitality | 2023 |
| Tenacity Vision Limited | Information & communication | 2025 |
| Tend and Flow Limited | Information & communication | 2025 |
| Tengma Equestrian Limited | Professional & scientific | 2019 |
| TES Retail Ltd. | Wholesale & retail | 2019 |
| Tesserae Advisory Ltd | Information & communication | 2026 |
| Texho Collection Ltd | Wholesale & retail | 2021 |
| TFS Partners Ltd | Information & communication | 2026 |
| TG Renewables Limited | Professional & scientific | 2026 |
| Thames Fire Ltd | Public administration | 2021 |
| THE Abundance Evolution Limited | Information & communication | 2024 |
| THE Ataxia-Telangiectasia Society | Health & social care | 2004 |
| THE Automated Customs and International Trade Association | Information & communication | 1985 |
| THE BAD Mums Club Ltd | Other services | 2023 |
| THE Bamboo Sock Company Ltd | Wholesale & retail | 2021 |
| THE Banking Centre Limited | Financial services | 2006 |
| THE Berkley Group Limited | Wholesale & retail | 2024 |
| THE Bourne Salisbury Avenue Harpenden Management Company Limited | Households | 2001 |
| THE Bourne Townsend Lane Harpenden Management Company Limited | Real estate | 2001 |
| THE BPM Group Limited | Information & communication | 2019 |
| THE Bridal Makeup Academy Ltd | Education | 2019 |
| THE Broken Golf Club Ltd | Professional & scientific | 2024 |
| THE Building Specialists Ltd | Construction | 2024 |
| THE Bull Whitwell Limited | Hospitality | 2013 |
| THE Burger Box Harpenden Ltd | Hospitality | 2023 |
| THE Cambridge Mortgage Company Limited | Financial services | 2021 |
| THE CH Consultancy Group Ltd | Professional & scientific | 2024 |
| THE Cobham Furniture Centre Limited | Wholesale & retail | 2012 |
| THE Combination Club Limited | Arts & recreation | 2023 |
| THE Countrifi Group Ltd | Wholesale & retail | 2021 |
| THE Crow (Fishpool Street) Management Company Ltd | Households | 2017 |
| THE CVC Club Ltd | Information & communication | 2025 |
| THE Deal Coach Limited | Professional & scientific | 2023 |
| THE Denture Clinic (Harpenden) Limited | Health & social care | 2006 |
| THE Double Glazing Doctor Essex Limited | Other services | 2019 |
| THE Educated Athlete Ltd | Education | 2025 |
| THE Energy Saving Centre Limited | Information & communication | 2022 |
| THE Fine Diamond, Jewellery & Watch Co Limited | Wholesale & retail | 2016 |
| THE Finesse Company Group Limited | Construction | 2022 |
| THE Food Teacher Ltd | Education | 2013 |
| THE Foot Clinic Harpenden Limited | Health & social care | 2025 |
| THE Foresters Freehold Ltd | Households | 2017 |
| THE Fragrant Dispensary Ltd | Health & social care | 2022 |
| THE Future IS Bright | Financial services | 2016 |
| THE Gaming Nexus Studios Ltd | Manufacturing | 2022 |
| THE Goode Kitchen Ltd | Hospitality | 2020 |
| THE Grove Mill Ltd | Information & communication | 2020 |
| THE Growth LAB Limited | Professional & scientific | 2013 |
| THE Harrow Harpenden Management Company Limited | Construction | 2019 |
| THE Hertfordshire Landscaping Company Ltd | Administrative & support | 2021 |
| THE HGV Crowd Limited | Administrative & support | 2025 |
| THE Hidden Grove Hair & Healing Ltd | Other services | 2026 |