| Joining Hands Healthcare Ltd | Public administration | 2021 |
| Joint Application Development Enterprises Limited | Information & communication | 1999 |
| Jonathan GT Adams Ltd | Health & social care | 2023 |
| Jordan Bespoke Limited | Professional & scientific | 2017 |
| Journey Mortgages Ltd | Financial services | 2019 |
| Joy Shakespeare Limited | Professional & scientific | 2018 |
| Joynes House Management Limited | Real estate | 2023 |
| JPD Travel Limited | Transport & logistics | 2015 |
| JPS Calibration Services Limited | Professional & scientific | 2005 |
| JPW Plumbing & Heating Limited | Construction | 2015 |
| JRG Eastwood Ltd | Financial services | 2025 |
| JRJ Management Ltd | Professional & scientific | 2021 |
| JRL3G Holdings Limited | Financial services | 2013 |
| JSM Vending Limited | Hospitality | 2022 |
| Jtab Ltd | Information & communication | 2018 |
| JTK Care Ltd | Health & social care | 2017 |
| Jules Services Ltd. | Other services | 2020 |
| Julia and Jaden LLP | | 2025 |
| Julie Tiley Consultancy Ltd | Professional & scientific | 2018 |
| Jumanuèl Limited | Health & social care | 2025 |
| Jump Twist Ltd | Wholesale & retail | 2025 |
| Junction 16 Sales & Rentals Ltd | Wholesale & retail | 2021 |
| JUNCTION56 Ltd | Transport & logistics | 2022 |
| Junior Rags Limited | Wholesale & retail | 2018 |
| Jura Homes Ltd | Real estate | 2021 |
| Just DO IT Consultants Ltd | Professional & scientific | 2016 |
| Just Flat Roof Ltd | Construction | 2018 |
| JVC Property LLP | | 2023 |
| JWB Holdings Limited | Financial services | 2022 |
| Jwine Reserve Limited | Wholesale & retail | 2023 |
| JWS Marking Limited | Professional & scientific | 2020 |
| JXH Services Ltd | Professional & scientific | 2020 |
| K & G Partners Ltd | Professional & scientific | 2022 |
| K a Holdings Limited | Professional & scientific | 2001 |
| K Scaffolding Limited | Construction | 2003 |
| K W Racing Ltd | Professional & scientific | 2017 |
| K.W. Motorsport Limited | Administrative & support | 2003 |
| K2 Recruitment Limited | Administrative & support | 1997 |
| KA Nest Project Ltd | Real estate | 2026 |
| Kabayan Capital Ltd | Financial services | 2012 |
| Kachoka Investments Limited | Real estate | 2020 |
| Kairos 23 Limited | Hospitality | 2023 |
| Kalehurst Garden Machinery Limited | Wholesale & retail | 1998 |
| Kalexis Solutions Ltd | Information & communication | 2025 |
| Kallal Trading Co UK Ltd | Manufacturing | 2019 |
| Karin Tindall Weddings Ltd | Administrative & support | 2025 |
| Karj Curated Investments Ltd | Administrative & support | 2025 |
| Karj Properties Ltd | Real estate | 2025 |
| Karj Property LLP | | 2024 |
| Karma Engineering Ltd | Professional & scientific | 2023 |
| Karnac Books Limited | Information & communication | 2017 |
| Karuwa Limited | Hospitality | 2025 |
| Katalba Property Investors Limited | Real estate | 2024 |
| Katchside Developments Ltd | Construction | 2026 |
| Katherine North London Ltd | Manufacturing | 2025 |
| KAW Services Ltd | Information & communication | 2006 |
| KB Services Oxford Ltd | Administrative & support | 2026 |
| KB Solutions(Uk) Ltd | Other services | 2023 |
| KB Thread Haven Ltd | Manufacturing | 2025 |
| KEA Consulting Ltd | Professional & scientific | 2023 |
| Keeconsult Limited | Information & communication | 2015 |
| Kel-Berg Contracts Limited | Administrative & support | 1994 |
| Kel-Berg Trailer and Trucks Limited | Wholesale & retail | 1991 |
| Kel-Berg Used Limited | Wholesale & retail | 2012 |
| Kelliher Building & Landscaping Ltd | Construction | 2026 |
| Kelliher Group Ltd | Financial services | 2026 |
| Kelliher Property Group Limited | Real estate | 2025 |
| Kelly (UK) Limited | Administrative & support | 2001 |
| Kellys Vegies Limited | Hospitality | 2011 |
| Kelyco Limited | Professional & scientific | 2018 |
| KEN Chim Hair UK Limited | Other services | 2024 |
| KEN Okuyama Design UK Limited | Professional & scientific | 2009 |
| Kendrick Electrical Services Ltd. | Construction | 2019 |
| Kensit Business Solutions Limited | Wholesale & retail | 2021 |
| Kensit Developments Limited | Real estate | 2019 |
| Kenzoll Energy Partners Ltd | Financial services | 2024 |
| Kerr Residential Ltd | Real estate | 2026 |
| Keys of Eden Foundation for Ecological Restoration and Radionics | Education | 1985 |
| Keystone Archaeology Ltd | Professional & scientific | 2024 |
| Keystone Construction & Renovations Ltd | Construction | 2025 |
| Killearn Properties Limited | Real estate | 2003 |
| Kiln Consulting LLP | | 2024 |
| KIM Swallowe Ltd | Professional & scientific | 2020 |
| Kim's Auto's Limited | Wholesale & retail | 2024 |
| Kim's MOT Centre Limited | Wholesale & retail | 2026 |
| Kimber & Sons Construction Limited | Construction | 2015 |
| Kimnu Property Ltd | Real estate | 2022 |
| Kinetica DB Limited | Administrative & support | 2016 |
| Kings Garden Centres Limited | Construction | 1961 |
| Kingsbury Racing Engines Ltd | Professional & scientific | 2019 |
| Kingsfivebarber Ltd | Other services | 2023 |
| Kingsgate Group Ltd | Water & waste | 2025 |
| Kingsmere Cars Bicester Ltd | Transport & logistics | 2019 |
| Kingsmere Community Centre C.I.C. | Other services | 2018 |
| Kingsmere Plumbing and Heating Ltd | Construction | 2020 |
| Kira Space Ltd | Health & social care | 2024 |
| Kismet Property Ltd | Real estate | 2024 |
| Kitchen Solutions (Thames Valley) Limited | Wholesale & retail | 2002 |
| Kitchen Sync Group Ltd | Hospitality | 2019 |
| Kittitian Properties Limited | Real estate | 2004 |