| JHR Horses Ltd | Arts & recreation | 2020 |
| JI Wandsor UK Ltd | Hospitality | 2022 |
| Jiana Capital Ltd | Real estate | 2018 |
| Jigsaw Cloud Ltd | Information & communication | 2000 |
| Jimm Traders Ltd | Wholesale & retail | 2025 |
| JJ Joinery Project Ltd | Manufacturing | 2014 |
| Jjpm Ltd | Health & social care | 2018 |
| JK Sales Consultancy Ltd | Professional & scientific | 2017 |
| JL Beauty & Aesthetics Ltd | Other services | 2024 |
| JLC Properties & Services Ltd | Real estate | 2025 |
| JLH Wealth Management Limited | Financial services | 2013 |
| JLR Engine Limited | Wholesale & retail | 2022 |
| Jlvc Limited | Administrative & support | 2020 |
| JM Steels Limited | Manufacturing | 2005 |
| JO Scott Images Limited | Professional & scientific | 2021 |
| Jonas Consulting Ltd | Administrative & support | 2019 |
| Joogynet Ltd | Education | 2009 |
| Joseph's Dream Co Limited | Construction | 2026 |
| Journey Counselling Ltd | Health & social care | 2021 |
| Journey MCS Limited | Administrative & support | 2012 |
| JRB Motor Sales Ltd | Wholesale & retail | 2025 |
| JRT Events Ltd | Administrative & support | 2025 |
| JRW & Sons Limited | Water & waste | 2003 |
| JS Flynn Limited | Wholesale & retail | 2024 |
| JS Global Consulting Limited | Administrative & support | 2016 |
| JS Randhawa Properties Limited | Real estate | 2026 |
| JSB Sterling (Development) Ltd | Real estate | 2023 |
| JSM Auto Limited | Wholesale & retail | 2024 |
| JSS Slough Limited | Professional & scientific | 2010 |
| Jstr Ltd | Other services | 2023 |
| JSW Consulting UK Ltd | Professional & scientific | 2008 |
| JTM Advisory Ltd | Information & communication | 2024 |
| JUN LIN Ltd | Hospitality | 2023 |
| June Warwick Limited | Professional & scientific | 2018 |
| Juniper Court (Chorleywood) Limited | Households | 2007 |
| Juno Capital Ltd | Real estate | 2021 |
| Jupiter Properties and Estates Limited | Construction | 1996 |
| Just Caversham Developments Ltd | Construction | 2017 |
| Just Golf Academy Limited | Arts & recreation | 2026 |
| Just Golf Holdings Limited | Financial services | 2024 |
| Just Golf Limited | Education | 2007 |
| Just Golf London Limited | Arts & recreation | 2015 |
| Just Golf Morpeth Limited | Arts & recreation | 2008 |
| Just Golf Nottingham Limited | Arts & recreation | 1999 |
| Just Golf Swadlincote Limited | Arts & recreation | 2015 |
| Juxtapose Design Limited | Information & communication | 2006 |
| JW Hill Garden Care Ltd | Administrative & support | 2011 |
| JZ Foods Ltd | Hospitality | 2023 |
| K & S Virdee Management Limited | Real estate | 2024 |
| K and a Cars Ltd | Administrative & support | 2017 |
| K&M Auto Techniks Ltd | Wholesale & retail | 2009 |
| K&M Housing Services Limited | Real estate | 2024 |
| K-Bod Investment Ltd | Real estate | 2022 |
| Kairos Camberley Ltd | Construction | 2026 |
| Kairos Development Ltd | Professional & scientific | 2019 |
| Kairos Estates Capital Ltd | Construction | 2025 |
| Kakkar Real Estate Ltd | Real estate | 2018 |
| Kalphena Partners Limited | Professional & scientific | 2026 |
| Kalshi UK Limited | Administrative & support | 2026 |
| Kamanja Limited | Hospitality | 2017 |
| Kaplan 1230 Property Ltd | Real estate | 2022 |
| Karl Perkins Limited | Professional & scientific | 2026 |
| Kate Davis Strategy Ltd | Information & communication | 2019 |
| Kate Group Ltd | Administrative & support | 2022 |
| Katie Baker Holdings Limited | Financial services | 2025 |
| Kaycee Environmental, Quality and Safety Consultancy Ltd | Professional & scientific | 2010 |
| KAZ Developments Ltd | Construction | 2021 |
| Kazzr Consulting Limited | Professional & scientific | 2022 |
| Kazzr Ltd | Real estate | 2019 |
| KB Film Services Ltd | Professional & scientific | 2012 |
| KB Law Solicitors Ltd | Professional & scientific | 2016 |
| Kbros Limited | Real estate | 2009 |
| KC Chauffeur Ltd | Transport & logistics | 2026 |
| Keelaro Ltd | Professional & scientific | 2014 |
| Keen Consultancy Services Ltd | Professional & scientific | 2023 |
| Keigan Business Services Limited | Administrative & support | 2016 |
| Kelston House UK Limited | Wholesale & retail | 2023 |
| Kenoch Asset Management Ltd | Construction | 2021 |
| Kensington Design & Build Ltd | Construction | 2024 |
| Kensington Heights (Freehold) Limited | Households | 2024 |
| Kensington Heights Management Company Limited | Households | 1998 |
| Kensington Lodge Management Company Limited | Households | 2006 |
| Kenth Consulting Ltd | Administrative & support | 2019 |
| Keystone Property Partners Ltd | Real estate | 2024 |
| KG Gardens Ltd | Administrative & support | 2023 |
| KG Metal Roofing Company Ltd | Construction | 2025 |
| Khelectrics Ltd | Professional & scientific | 2025 |
| Khyatiyash Properties and Investments Ltd | Real estate | 2020 |
| Killoran Agriworks Ltd | Construction | 2024 |
| Kimbers Farm Equestrian Ltd | Agriculture & fishing | 2025 |
| Kindred Concepts Europe Limited | Hospitality | 2023 |
| King Homecare Ltd | Health & social care | 2020 |
| King's Ride Residents Limited | Households | 1951 |
| Kingfisher Hill Limited | Health & social care | 2009 |
| Kingfisher Place Residents Management Company Limited | Households | 2020 |
| Kingsacre Cookham Limited | Administrative & support | 2016 |
| Kingsacre Riverside Limited | Administrative & support | 2016 |
| Kingsacre Slough Limited | Administrative & support | 2016 |
| Kingsbury Systems Limited | Information & communication | 2011 |
| Kingsmead (Slough) Management Company Limited | Households | 2004 |