| Home Affairs Interior Design Ltd | Wholesale & retail | 2014 |
| Hook-Up Solutions Limited | Administrative & support | 2015 |
| Htcfc | Arts & recreation | 2016 |
| Hunt and Handa Investments Ltd | Construction | 2024 |
| Hunt Consulting Services Limited | Professional & scientific | 2015 |
| Hunt Lightfoot Investments Limited | Real estate | 2015 |
| Hunt Property Investments Ltd | Real estate | 2013 |
| IA Real Estate Solutions Ltd | Professional & scientific | 2026 |
| Ibex Change & Transformation Limited | Professional & scientific | 2026 |
| Imber Financial Services Limited | Financial services | 2015 |
| IMJ Legal Metrology Consultants Ltd | Professional & scientific | 2021 |
| Infinity Gifting Ltd | Wholesale & retail | 2020 |
| Infomig Ltd | Information & communication | 2009 |
| Integra User Group Limited | Other services | 1994 |
| Investment Casting Mouldmakers Limited | Manufacturing | 2000 |
| Iverley Properties Limited | Construction | 1999 |
| IVY Procelain Ltd | Wholesale & retail | 2025 |
| J Whelan Associates Limited | Professional & scientific | 2005 |
| J&B Precise Air Lifting Systems Ltd | Professional & scientific | 2023 |
| J&D Fire Engineering Ltd | Professional & scientific | 2023 |
| J.C. Deaville Limited | | 1981 |
| Jacks Barrel Ltd | Hospitality | 2025 |
| James Construction Limited | Construction | 2006 |
| Januja PVT Ltd | Wholesale & retail | 2015 |
| JCA Unique Care Ltd | Health & social care | 2021 |
| Jelly Recruitment Limited | Administrative & support | 2023 |
| Jien Plant Based Healing Limited | Health & social care | 2026 |
| JNM Football Limited | Professional & scientific | 2024 |
| John Sale Residents Limited | Real estate | 2003 |
| John Stamford Consulting Ltd | Professional & scientific | 2024 |
| JSL Transport Limited | Transport & logistics | 2025 |
| Jtaylorweb Ltd | Information & communication | 2020 |
| Junction.London Limited | Professional & scientific | 2019 |
| Jungsa Limited | Transport & logistics | 2025 |
| Junior Haria Holdings Limited | Financial services | 2020 |
| Jupiter Technologies Ltd | Information & communication | 2025 |
| Jutla Consulting Ltd | Administrative & support | 2022 |
| JV Architecture Ltd | Professional & scientific | 2017 |
| JW Football Coaching Ltd | Education | 2024 |
| KAA Consultancy Services Limited | Information & communication | 2011 |
| Kara Manai Properties Ltd | Real estate | 2021 |
| Kendals Restoration Ltd | Other services | 2018 |
| Kenstar Investments Ltd | Financial services | 2025 |
| Kindlelight Windows Ltd | Construction | 2012 |
| Kings Mount Residents Management Co Limited | Households | 2012 |
| Kingsfield Baldock Ltd | Real estate | 2017 |
| Knkn Limited | Professional & scientific | 2019 |
| Kosi Homes Ltd | Real estate | 2019 |
| Kriya Digital Limited | Information & communication | 2024 |
| Kytone Ltd | Wholesale & retail | 2025 |
| L.N & G Indemnity Ltd | Financial services | 2017 |
| L.S.F. Properties Limited | Construction | 1998 |
| Laing Investments Partnership Limited | Real estate | 2023 |
| Lallimj Ltd | Hospitality | 2024 |
| Lamedos Ltd | Real estate | 2020 |
| Lannock Hinxworth Mental Health Limited | Health & social care | 2025 |
| Lauren Finney Limited | Health & social care | 2022 |
| Lavender Court (Baldock) Limited | Other services | 1991 |
| Lawrence Thorogood Ltd | Construction | 2023 |
| Laytonspar Ltd | Transport & logistics | 2019 |
| LEARN2DRIVEHUB Ltd | Wholesale & retail | 2025 |
| Ledifique Ltd | Manufacturing | 2018 |
| LEE Sharman Fencing Limited | Construction | 2005 |
| Leisuregrow Products Limited | Wholesale & retail | 1999 |
| Lesley & Co Holdings Ltd | Financial services | 2023 |
| Letchworth Plant Hire Limited | Manufacturing | 1992 |
| Level UP Financial Education CIC | Other services | 2019 |
| Lewis Banks & Sons (Engineers) Limited | Manufacturing | 1948 |
| Lewis Banks Limited | Manufacturing | 2002 |
| Liberty Bishop Financial Services Ltd | Financial services | 1999 |
| Life IS Rhythm Ltd | Education | 2024 |
| Lilac Box Company Limited | Administrative & support | 2020 |
| Linear Instruments Services Limited | Manufacturing | 2003 |
| Lintherm Limited | Extraterritorial | 2016 |
| Lionheart Coaching Limited | Education | 2024 |
| Little Cammocks Limited | Health & social care | 2026 |
| LLU Property Ltd | Real estate | 2022 |
| LNG Digital Limited | Information & communication | 2023 |
| London Road Audio Services Ltd | Information & communication | 2011 |
| London Road Event Hire Services Ltd | Administrative & support | 2022 |
| Loogistics Ltd | Administrative & support | 2024 |
| Lovell Kitchens Ltd | Construction | 2021 |
| LPP Construction Services Ltd | Construction | 2014 |
| LSF Property Holdings Limited | Real estate | 2021 |
| Ltsc Property Limited | Real estate | 2022 |
| LV Cleaning Ltd | Administrative & support | 2023 |
| M,A & E Holdings Limited | Real estate | 2024 |
| Mabert Enterprises Limited | Hospitality | 2023 |
| Maharaja Hospitality Limited | Hospitality | 2024 |
| Mallory QS Ltd | Professional & scientific | 2022 |
| Manage Care Homes Limited | Health & social care | 2005 |
| Mango Touring Ltd | Arts & recreation | 2022 |
| Mansfield Mews (Estate) Management Limited | Households | 2002 |
| Maple Tree Baldock Ltd | Construction | 2019 |
| Maxima Property Investment Ltd | Real estate | 2018 |
| Mccoles & Co (Herts) Ltd | Professional & scientific | 2021 |
| Mcnyes Ltd | Real estate | 2024 |
| Meadow Cottages Investment Ltd | Real estate | 2022 |
| Meadow Cottages Ltd | Real estate | 2022 |
| Megalith Software Limited | Information & communication | 1996 |