| Junktion Limited | Real estate | 2000 |
| Juno Capital Partners I LLP | | 2021 |
| Junus Limited | Hospitality | 2017 |
| Jupiter Management Limited | Construction | 2015 |
| Just for a Change Ltd | Professional & scientific | 2025 |
| Just Legal Search Ltd | Administrative & support | 2024 |
| Just Management Services Ltd | Other services | 2015 |
| Justcarbon Holdings Ltd | Professional & scientific | 2023 |
| Justin Craig Education Limited | Education | 1985 |
| Justrate Limited | Information & communication | 2023 |
| Justtheclick Ltd | Wholesale & retail | 2025 |
| JW Labs Ltd | Financial services | 2026 |
| JW Land Surveys Limited | Professional & scientific | 2017 |
| Jwcoaching Ltd | Professional & scientific | 2009 |
| Jwkd Holdings Ltd | Financial services | 2022 |
| JYO Consulting Limited | Information & communication | 2010 |
| JZG Technology Limited | Information & communication | 2020 |
| K & J Consultants Limited | Professional & scientific | 2007 |
| K & R Coachworks Limited | Wholesale & retail | 2006 |
| K Chauffeur Solution Ltd | Transport & logistics | 2022 |
| K J L Consultancy Ltd | Professional & scientific | 2011 |
| K K & L J Enterprises Limited | Professional & scientific | 2012 |
| K&G Costea Ltd | Construction | 2019 |
| K.D.P Services Ltd | Construction | 2024 |
| K.G Quant Ltd | Information & communication | 2019 |
| K16 Contracts Limited | Construction | 2006 |
| Kaak Holdings Limited | Financial services | 2021 |
| Kaimera Solutions Limited | Professional & scientific | 2014 |
| Kairos Modern Learning Limited | Professional & scientific | 2014 |
| Kajoch Design Limited | Administrative & support | 2011 |
| Kakoo & SON Limited | Professional & scientific | 2018 |
| Kale Concepts Limited | Health & social care | 2010 |
| Kalmea Limited | Extraterritorial | 2012 |
| Kalna Limited | Health & social care | 2011 |
| Kaloci Construction Ltd | Construction | 2022 |
| Kalpadrum Properties Limited | Real estate | 2023 |
| Kamadospace Limited | Wholesale & retail | 2020 |
| Kamarat Ltd | Wholesale & retail | 2023 |
| Kamco Limited | Manufacturing | 1984 |
| Kamur Developments Limited | Professional & scientific | 2016 |
| Kandour Growth Partners Ltd | Professional & scientific | 2024 |
| Kandui SPV LLP | | 2020 |
| Kane Investments Limited | Real estate | 2024 |
| Kapow - Dance Circus Theatre CIC | Education | 2020 |
| Kareela Ltd | Professional & scientific | 2001 |
| Karen Beale Ltd | Extraterritorial | 2024 |
| Karen Durkin Consulting Limited | Professional & scientific | 2013 |
| Karen Richards Therapy Ltd | Administrative & support | 2012 |
| Kariah Davids Consulting Ltd | Professional & scientific | 2018 |
| Karis Portfolio LLP | | 2026 |
| Karthik Rasa Ltd | Wholesale & retail | 2026 |
| Karukera Limited | Professional & scientific | 2025 |
| Kaskos Property Ltd | Real estate | 2017 |
| Kasons Services Limited | Administrative & support | 2012 |
| Kaspa Services Ltd. | Information & communication | 2011 |
| Kathryn Edwards Consulting Limited | Professional & scientific | 2023 |
| Katrina Keverne Limited | Professional & scientific | 2021 |
| Kave Quinn Design Ltd | Professional & scientific | 2026 |
| KAY Products Ltd | Professional & scientific | 2019 |
| Kayna Innovation UK Limited | Financial services | 2021 |
| Kazou Consultancy Ltd | Administrative & support | 2012 |
| KBS Holiday Lettings Ltd | Hospitality | 2023 |
| KBS Stayhub Ltd | Hospitality | 2023 |
| KC & Stones Consultants Ltd | Hospitality | 2022 |
| KC Investors Ltd | Construction | 2021 |
| KCH Nutrition Ltd | Hospitality | 2015 |
| KCM Media Limited | Information & communication | 2009 |
| Kcohen Limited | Wholesale & retail | 2022 |
| KD Wright Financial Services Holdings Limited | Financial services | 2020 |
| KD Wright Financial Services Limited | Financial services | 2000 |
| KD Wright Financial Services Topco Limited | Financial services | 2025 |
| Kdsfx Ltd | Information & communication | 2019 |
| KEA Computing Limited | Information & communication | 1987 |
| Keane Property Holding 2 Limited | Construction | 2015 |
| Keane Property Holding 3 Limited | Construction | 2019 |
| Keane Property Holding 4 Limited | Hospitality | 2023 |
| Keane Property Holding Limited | Wholesale & retail | 1928 |
| Kearney Bell Limited | Real estate | 2018 |
| Kearns Plant Limited | Administrative & support | 1973 |
| Keeler Property Ltd | Real estate | 2018 |
| Keep Cooking Ltd | Manufacturing | 2018 |
| Keepout Ltd | Administrative & support | 2008 |
| Keith Hills Construction Services Limited | Real estate | 2019 |
| Kelian Recruitment Ltd | Administrative & support | 2024 |
| Kelso Estates Ltd | Real estate | 2014 |
| Kempston Radiators Limited | Wholesale & retail | 2002 |
| KEN and Karsa Limited | Real estate | 2019 |
| KEN Hodson Computer Services Limited | Information & communication | 2004 |
| KEN Mchale & Associates Limited | Professional & scientific | 2000 |
| Kenbay Compaction Systems Limited | Extraterritorial | 2011 |
| Kenmore I.T. Ltd | Information & communication | 2007 |
| Kensington Training Club Limited | Arts & recreation | 2022 |
| Kenstanley Ltd | Professional & scientific | 2026 |
| Kent and London Limited | Manufacturing | 2015 |
| Kent Swimming LLP | | 2024 |
| Kento Property Solutions Ltd | Real estate | 2025 |
| Kerada Nominee Ltd | Real estate | 2017 |
| Kerai Properties Limited | Real estate | 2017 |
| Kernow Retreats Ltd | Hospitality | 2023 |
| Kernowcom Limited | Real estate | 2017 |