| J.Melbourne Hairdressing Limited | Financial services | 2026 |
| J.Sharpe Enterprises Limited | Real estate | 1971 |
| JA Apps Ltd | Administrative & support | 2024 |
| Jackson's of Harpenden Ltd | Construction | 2017 |
| Jacksons Commercial Properties Limited | Real estate | 1998 |
| JAD Property Refurbishment Ltd | Construction | 2020 |
| Jalecu Limited | Professional & scientific | 2025 |
| James Alexander Groom Ltd | Financial services | 2026 |
| James Braid Golf Limited | Extraterritorial | 1997 |
| James Charlotte Limited | Real estate | 2026 |
| James FCS Limited | Wholesale & retail | 2010 |
| Jane Holmes Limited | Hospitality | 2008 |
| Jang Studios Limited | Information & communication | 2018 |
| Jaysh Care Services Limited | Health & social care | 2016 |
| Jb's Pet Pantry Ltd | Wholesale & retail | 2018 |
| JBA Executive Recruitment Limited | Administrative & support | 2008 |
| JEB Construction Limited | Construction | 1995 |
| JEB Homes Ltd | Construction | 2020 |
| Jelly Fabrics Ltd | Manufacturing | 2021 |
| Jemimahire Ltd | Construction | 2026 |
| Jemka Consulting Limited | Professional & scientific | 2010 |
| Jenkyn Prevent Consultancy and Training Ltd | Administrative & support | 2019 |
| Jennie Green Acres Ltd | Agriculture & fishing | 2020 |
| Jenny Green Limited | Hospitality | 2016 |
| JF Homes Limited | Administrative & support | 2018 |
| JF Management Limited | Administrative & support | 2020 |
| Jisp Solutions Ltd | Wholesale & retail | 2020 |
| Jkwired Ltd | Construction | 2022 |
| JL Wilkinson Ltd | Professional & scientific | 2019 |
| JL8 (UK) Limited | Real estate | 2012 |
| John Constable Limited | Professional & scientific | 2013 |
| John Lewis Auto Services Ltd | Wholesale & retail | 2025 |
| Johnson Investment Properties Limited | Real estate | 1999 |
| Jollysgoods Ltd | Wholesale & retail | 2025 |
| Joseph Charles Limited | Other services | 1999 |
| JP Consulting Partners Ltd | Information & communication | 2019 |
| JP Whittaker Ltd | Professional & scientific | 2014 |
| JR Pizza Limited | Hospitality | 2022 |
| JT Fire Systems Ltd | Other services | 2021 |
| Jukaa Limited | Wholesale & retail | 2026 |
| Juniper Print Company Limited | Professional & scientific | 2014 |
| Just LIZ Limited | Other services | 2002 |
| JWM Farming Limited | Agriculture & fishing | 2024 |
| JWW Air Conditioning Limited | Construction | 2025 |
| JX5 Consulting Limited | Information & communication | 2015 |
| JX5 Investments Ltd | Financial services | 2026 |
| K J W Property Limited | Real estate | 2026 |
| K L Mckernan Ltd | Financial services | 2022 |
| K&E Hairdressing Limited | Other services | 2026 |
| K&T Lettings Limited | Real estate | 2019 |
| K. Walsh Electrical Limited | Construction | 2022 |
| K40 Design Limited | Professional & scientific | 2012 |
| Kabelia Limited | Construction | 1993 |
| Kaighin & Daughter Limited | Wholesale & retail | 1965 |
| Kakura Properties Ltd | Real estate | 2025 |
| Karl Moore Plumbing and Heating Limited | Construction | 2021 |
| Katherine Lindsay Services Limited | Education | 2025 |
| Kathy Lewis Weddings Limited | Administrative & support | 2025 |
| Kaybee Consultancy Ltd | Information & communication | 2015 |
| KB Instrumentation Software Limited | Administrative & support | 2011 |
| KB Property and Investments Limited | Real estate | 2019 |
| Kealy Properties Ltd | Real estate | 2013 |
| Kebomed UK Ltd. | Wholesale & retail | 2005 |
| Kecollingborn Limited | Hospitality | 2025 |
| Keep IT Simple Solutions Limited | Information & communication | 2005 |
| Keith Gott Limited | Professional & scientific | 2017 |
| Kelsafe Management Services Ltd | Other services | 2017 |
| Kenelm Hospitality Limited | Hospitality | 2015 |
| Kensington (T) Hairdressing Limited | Other services | 2020 |
| Kerry Jane Designs Ltd | Professional & scientific | 2014 |
| Kerry SR Ltd | Professional & scientific | 2024 |
| KFJ Groundcare Ltd | Administrative & support | 2024 |
| KG Hypnobirthing Ltd | Health & social care | 2008 |
| Kiddotech Ltd | Wholesale & retail | 2024 |
| KIM Taylor Sustainability Consulting Ltd | Professional & scientific | 2023 |
| Kinetica Pro Consult Ltd | Professional & scientific | 2023 |
| Kingsmarque Limited | Construction | 2026 |
| Kingston (T2) Hairdressing Limited | Other services | 2004 |
| Kismat Renovations Ltd | Construction | 2024 |
| KJN Developments (Alton) Limited | Real estate | 1985 |
| KM & MK Investments Ltd | Real estate | 2021 |
| KMH Controls Ltd | Professional & scientific | 2019 |
| Knowles Industries (UK) Limited | Financial services | 2019 |
| Knutsford (T) Hairdressing Limited | Other services | 2007 |
| Kognitive Consulting Ltd | Information & communication | 2023 |
| Koolair Technical Services Ltd | Other services | 2006 |
| Kozmos Wine Ltd | Manufacturing | 2025 |
| Ktjb Limited | Real estate | 2016 |
| KTR Management Ltd | Real estate | 2003 |
| Kunjalo Limited | Administrative & support | 2024 |
| Kwts Limited | Information & communication | 2002 |
| L & C Holdings (Hampshire) Limited | Other services | 2017 |
| L Goodes Roofing Ltd | Construction | 2018 |
| L T S Building Services Limited | Construction | 1996 |
| L. Kharitonova Limited | Professional & scientific | 2014 |
| LA Societe Apparel Limited | Wholesale & retail | 2014 |
| Label.M Products Limited | Other services | 2010 |
| Laboratory Instrumentation Limited | Professional & scientific | 2015 |
| Lacane Solutions Limited | Other services | 2016 |
| Laddad Industries Ltd | Wholesale & retail | 2025 |