| Imogen's Canine Theracare Ltd | Other services | 2023 |
| Independent Contract Lifting Services Limited | Construction | 2015 |
| Independent Traffic Solutions Ltd | Administrative & support | 2025 |
| Inis Communication Limited | Administrative & support | 2009 |
| Inmedix UK Ltd | Professional & scientific | 2017 |
| Invicta Associates Ltd | Professional & scientific | 2021 |
| Iordache Holdings Ltd | Financial services | 2019 |
| IQ Property & Business Solutions Ltd | Real estate | 2001 |
| Iron Grip Engineering Ltd | Wholesale & retail | 2024 |
| Italian Furniture Distribution Limited | Wholesale & retail | 2022 |
| Italiano Connection Ltd | Wholesale & retail | 2025 |
| J & K Knitwear Co Limited | Wholesale & retail | 1995 |
| J D Initiatives Limited | Information & communication | 2003 |
| J E S Administration Ltd | Real estate | 2003 |
| J S Plastering (Luton) Limited | Construction | 2007 |
| J. Day Stoneworks Limited | Wholesale & retail | 2003 |
| J.P. Broadcast Network Services Ltd. | Information & communication | 2016 |
| JAB Associates Limited | Administrative & support | 1990 |
| Janu Limited | Wholesale & retail | 2007 |
| JB Colbert Ltd | Information & communication | 2020 |
| JDB Enterprise Property Limited | Real estate | 2016 |
| JED Skelton Consulting Ltd | Information & communication | 2021 |
| Jeffersons Jemnics Limited | Real estate | 1997 |
| Jemcroft Consultancy Limited | Professional & scientific | 2008 |
| JIB Skiing Limited | Arts & recreation | 2016 |
| Joanna Adolph Coaching Ltd | Professional & scientific | 2024 |
| Johnson Blythe (Harpenden) Limited | Other services | 2022 |
| Johnson Blythe Limited | Other services | 2016 |
| JOM Cork Ltd | Real estate | 2023 |
| JON Cartwright Photography Ltd | Professional & scientific | 2012 |
| Jotom Investment Limited | Real estate | 1995 |
| JSS Test Management Consultancy Limited | Information & communication | 2014 |
| JTB Property Services LLP | | 2023 |
| Judicare Law International Limited | Professional & scientific | 2016 |
| Juniper Gardens Residents Association Limited | Real estate | 1985 |
| Just ASK Recruitment Ltd | Administrative & support | 2023 |
| Just Experience Ltd | Hospitality | 2024 |
| Justbite Limited | Administrative & support | 2009 |
| K Matthews Surveying Services Ltd | Professional & scientific | 2026 |
| K.A. Lock & Partners Limited | Wholesale & retail | 1982 |
| K.M. Property Limited | Real estate | 1990 |
| K9 Cuisine Ltd | Wholesale & retail | 2011 |
| Kandi Pubs Ltd | Hospitality | 2022 |
| Katalyst Consulting Limited | Professional & scientific | 2016 |
| Kathleen’S Candy Creations Limited | Hospitality | 2025 |
| Katia Perez Design Ltd | Professional & scientific | 2022 |
| Kcns Group Ltd | Wholesale & retail | 2019 |
| KDR Property Ltd | Real estate | 2026 |
| KDT (UK) Limited | Wholesale & retail | 2009 |
| Keith Piggott Property Ltd | Construction | 2013 |
| Keithug Limited | Real estate | 2009 |
| KELFIELD63 Limited | Professional & scientific | 2015 |
| Kellstar Capital Ltd | Financial services | 2023 |
| Kellstar Ltd | Professional & scientific | 2018 |
| Keygo Limited | Real estate | 2019 |
| Kf-Prop Ltd | Wholesale & retail | 2019 |
| Kidmono Ltd | Wholesale & retail | 2025 |
| Kline Capital Investment Commercial Limited | Real estate | 2022 |
| Kline Capital Investments Ltd | Real estate | 2017 |
| KMS Property & Development Ltd | Real estate | 2022 |
| Koospol, Foreign Trade Company Limited | Wholesale & retail | 2019 |
| Kstutoring Ltd | Information & communication | 2021 |
| Kurz & Sullivan Ltd | Financial services | 2021 |
| L & J Property Portfolio Limited | Real estate | 2022 |
| L P H Solutions Ltd | Financial services | 2010 |
| L&Jb Properties Ltd | Real estate | 2025 |
| L&R Medics Limited | Health & social care | 2012 |
| L.J. Whiteman & SON Limited | Extraterritorial | 2005 |
| L.K.B. Building Company Limited | Construction | 1975 |
| Laamab Limited | Real estate | 2013 |
| Ladywalk LLP | | 2015 |
| Laleham Lodge Ltd | Professional & scientific | 2024 |
| Lambert Scaffolding Ltd | Construction | 2014 |
| Landor Developments Ltd | Construction | 2022 |
| Lanercost Limited | Professional & scientific | 2011 |
| Laurence Joseph Penn Ltd | Extraterritorial | 2022 |
| Lbwp Limited | Professional & scientific | 2009 |
| Let's Dance Academy Ltd | Education | 2019 |
| Leto Brothers Limited | Other services | 2008 |
| Lily Molly Properties Ltd | Real estate | 2022 |
| Limbs & Trims Ltd | Administrative & support | 2025 |
| Limebrook Limited | Administrative & support | 2015 |
| Limitex Ltd | Administrative & support | 2019 |
| Listi Ltd | Information & communication | 2025 |
| Little Enterprise Group Ltd | Construction | 2026 |
| Living Eggs (Herts) Limited | Education | 2017 |
| LJW Estates Ltd | Real estate | 2025 |
| LKB Rose Consulting Limited | Professional & scientific | 2024 |
| Lluxe Living Ltd | Households | 2024 |
| LM Accounting Ltd | Professional & scientific | 2026 |
| LMC Highway Design Ltd | Construction | 2026 |
| LMP Business Services Ltd | Professional & scientific | 2017 |
| Lobster POT Events Ltd | Hospitality | 2022 |
| Lohm Ltd | Information & communication | 2022 |
| London Techworks Limited | Information & communication | 2017 |
| LR Motor Group Limited | Wholesale & retail | 2024 |
| Lucy B Creative Limited | Professional & scientific | 2025 |
| Luke Warren Limited | Wholesale & retail | 2016 |
| Lumo Ventures Ltd | Financial services | 2021 |
| Luther Medical Ltd | Health & social care | 2024 |