| Intellisparks Electrical Services Limited | Construction | 2013 |
| Intent Marketing Ltd | Professional & scientific | 1998 |
| Interglow (Contracts) Limited | Construction | 1986 |
| Interglow Limited | Real estate | 1982 |
| International Association for Digital Publications | Education | 2004 |
| International Stem Cell Biobanking Initiative | Education | 2023 |
| Interprise Limited | Extraterritorial | 1988 |
| Investment Growth Club UK Ltd | Professional & scientific | 2022 |
| Invictus Foresight Protection Ltd | Administrative & support | 2016 |
| ION Science Limited | Manufacturing | 1989 |
| IQ121.COM Limited | Wholesale & retail | 2023 |
| Iqxpand Limited | Professional & scientific | 2024 |
| IRC B Ltd | Professional & scientific | 2018 |
| Ireland Express Limited | Transport & logistics | 2008 |
| Iron Door Film Company Limited | Information & communication | 2013 |
| Iron Hive Ltd | Arts & recreation | 2023 |
| Isabel & INK Limited | Other services | 2016 |
| Isatek Limited | Wholesale & retail | 2002 |
| Isleglade Limited | Construction | 1991 |
| J & a Perry Ltd | Real estate | 2015 |
| J a D Farming LLP | | 2018 |
| J Carter & Co(Lime Street)(Holdings)Limited | Financial services | 1948 |
| J F Rees Limited | Professional & scientific | 2010 |
| J Faime Limited | Information & communication | 2003 |
| J J & a Trading Limited | Administrative & support | 2021 |
| J Jeffrey & SON Limited | Manufacturing | 2003 |
| J P a Investments Limited | Extraterritorial | 2012 |
| J Ramshaw Pharm Ltd | Health & social care | 2025 |
| J Sell Curations Ltd | Wholesale & retail | 2025 |
| J&D Electrical Engineering Limited | Real estate | 2017 |
| J. Tiburcio Limited | Health & social care | 2023 |
| J.A. Clayton Limited | Agriculture & fishing | 1960 |
| J.J.A.Y GAS & OIL Heating Services Limited | Construction | 2016 |
| J.S.Kell Consultancy Services Ltd | Construction | 2024 |
| J.W.Padfield Limited | Agriculture & fishing | 1957 |
| Jack Hooper Ltd | Transport & logistics | 2024 |
| Jack Squirrel Property Limited | Real estate | 2019 |
| Jade Phoenix Ltd | Real estate | 2015 |
| JAG Security Solutions Ltd | Administrative & support | 2017 |
| Jalice Interactive Ltd | Information & communication | 2025 |
| James Dyer Antiques Limited | Administrative & support | 2001 |
| James-Tech Limited | Information & communication | 2020 |
| Jamie Porter Limited | Wholesale & retail | 2002 |
| Jamila Consultancy Services Ltd | Construction | 2021 |
| Jane Clemetson Limited | Professional & scientific | 2010 |
| Janeteva Consultants Limited | Professional & scientific | 2026 |
| Jasper Solutions Limited | Information & communication | 2008 |
| Jay’S Vehicles Ltd | Wholesale & retail | 2026 |
| JB PDR Ltd | Wholesale & retail | 2022 |
| JBP Advisory Ltd | Professional & scientific | 2025 |
| JC Frost Engineering Limited | Professional & scientific | 2023 |
| JC Majestic Property's Ltd | Construction | 2025 |
| JCM Brickwork and Landscaping Limited | Construction | 2023 |
| JCW Group Limited | Financial services | 2017 |
| JD Electrical and Building Limited | Construction | 2018 |
| JDH Farms Ltd | Agriculture & fishing | 1999 |
| JDM 88 Ltd | Wholesale & retail | 2019 |
| JDM 888 Limited | Extraterritorial | 2018 |
| Jennys Repairs & Alterations Ltd | Other services | 2009 |
| JES Services Limited | Professional & scientific | 2016 |
| Jesse's Cars Ltd | Wholesale & retail | 2023 |
| JET Clean Masters Ltd | Administrative & support | 2025 |
| Jgmb Consulting Limited | Professional & scientific | 2015 |
| JHE Electrical Contractors Ltd | Construction | 2003 |
| Jing Gang (UK) Limited | Hospitality | 2022 |
| JJ Developments Sawbridgeworth LLP | | 2025 |
| Jjfw Consulting Limited | Professional & scientific | 2012 |
| Jjmco Limited | Financial services | 2025 |
| JLH Realty Limited | Real estate | 2024 |
| JNB Plumbing & Heating Limited | Construction | 2019 |
| JNL Property Management and Maintenance Ltd | Construction | 2021 |
| JOE Graves Design Ltd | Administrative & support | 2023 |
| Jofa Holdings Limited | Manufacturing | 2022 |
| John Blair Consult Limited | Professional & scientific | 2022 |
| John Cobb & Sons Limited | Construction | 1971 |
| John Deed Ltd | Administrative & support | 2010 |
| John Harrison Investment Consulting Limited | Financial services | 2013 |
| John Wahlich Associates Limited | Professional & scientific | 2011 |
| Johnstone Products Limited | Wholesale & retail | 2023 |
| JON Newis (UK) Limited | Financial services | 2011 |
| Jones Brothers Construction Ltd | Construction | 2019 |
| Joy Cafe Ltd | Hospitality | 2026 |
| JR & DC Enterprises Limited | Wholesale & retail | 1999 |
| JR Technology Limited | Manufacturing | 1983 |
| JRA Associates Ltd. | Professional & scientific | 2011 |
| Jrmassociatesuk Limited | Professional & scientific | 2018 |
| JS Aesthetica Ltd | Health & social care | 2023 |
| JS Fencing Limited | Administrative & support | 2013 |
| JS Lead GEN & Marketing Solutions Ltd | Professional & scientific | 2024 |
| Julian Court Freehold Company Limited | Households | 2006 |
| Julianprice.Com Ltd | Agriculture & fishing | 2018 |
| Juliet Creates Limited | Professional & scientific | 2022 |
| Just Plane Trading Limited | Wholesale & retail | 2001 |
| Just Women Network Ltd | Administrative & support | 2026 |
| JW Precision Limited | Manufacturing | 1998 |
| JWA Surveyors Ltd | Professional & scientific | 2025 |
| K B Marketing Services Ltd | Construction | 2008 |
| K B Property Management Ltd | Real estate | 2013 |
| K Empire Residence Ltd | Real estate | 2024 |
| K M Exhausts Limited | Manufacturing | 2012 |