| James Micklewright & Associates Limited | Professional & scientific | 2010 |
| Jamie Smith Estates Limited | Construction | 1998 |
| Jamie Smith Investments Ltd | Construction | 2020 |
| Janda Holder Limited | Other services | 2023 |
| Jane Cottrell Consulting Ltd | Professional & scientific | 2019 |
| Japan Connect Limited | Professional & scientific | 2013 |
| JAY & JAI Investments Limited | Real estate | 2025 |
| JC & Co Boatworks Limited | Manufacturing | 2024 |
| JC Accounting Resources Ltd | Professional & scientific | 2024 |
| JD Residential Ltd | Construction | 2018 |
| JDA Properties Limited | Construction | 2007 |
| Jefferies Accountancy Services Ltd | Professional & scientific | 2004 |
| Jefferies Land Ltd | Real estate | 2017 |
| Jefferies Probate Ltd | Professional & scientific | 2019 |
| Jenner Developments Limited | Construction | 2023 |
| Jenner Estates Group Limited | Real estate | 2022 |
| Jenny's Accounting Services Ltd | Professional & scientific | 2018 |
| Jenova Creative Limited | Information & communication | 2017 |
| Jenova Limited | Information & communication | 1994 |
| JEX Construction Limited | Construction | 1975 |
| JEX Developments Limited | Construction | 1988 |
| Jezcam Limited | Professional & scientific | 2012 |
| JG Tyre and Exhausts Limited | Wholesale & retail | 2026 |
| Jhra Ltd | Professional & scientific | 2014 |
| Jiggens Estates Limited | Real estate | 2021 |
| Jiggens Property Limited | Construction | 2017 |
| JJB & Sons Limited | Hospitality | 2017 |
| JL Performance Limited | Professional & scientific | 2023 |
| JL Sports Management Ltd | Arts & recreation | 2019 |
| JLE Plumbing and Heating Limited | Construction | 2016 |
| JLM Partnership LLP | | 2009 |
| JLP Business Consultants Limited | Professional & scientific | 2021 |
| Jlwalker Design Ltd | Professional & scientific | 2018 |
| Jmjl Properties Ltd | Real estate | 2026 |
| JMS Business Services Limited | Professional & scientific | 2016 |
| JO Wise Design Ltd | Professional & scientific | 2024 |
| John Glen Films Limited | Information & communication | 1964 |
| John Howard ( Collingbourne) Limited | Financial services | 2020 |
| John Howard (Bothwell) Limited | Construction | 2022 |
| John Howard (Fife) Limited | Construction | 2022 |
| John Howard (Northwood) Limited | Financial services | 2020 |
| John Howard (Stirling) Limited | Financial services | 2020 |
| John Howard (Wakefield) Limited | Financial services | 2020 |
| John Howard Investments Limited | Real estate | 2020 |
| Johnson Agri-Plant Ltd | Wholesale & retail | 2024 |
| Joint Ventures (Holdings NO.1) Limited | Financial services | 2016 |
| Jomablue Ltd | Information & communication | 2024 |
| Jonas Property Media Ltd | Professional & scientific | 2021 |
| Jonathan Blain Ltd | Professional & scientific | 2026 |
| Jonkers Limited | Wholesale & retail | 2004 |
| Jonwakefield Ltd | Professional & scientific | 2025 |
| Joshua Farnsworth Holdings Limited | Financial services | 2025 |
| JOW Investments Limited | Real estate | 2016 |
| JR Global Investments Ltd | Financial services | 2017 |
| JS Bowie Limited | Professional & scientific | 2023 |
| JS Motor Works Ltd | Wholesale & retail | 2015 |
| JSS Rowing Ltd | Professional & scientific | 2025 |
| Jtech Automotive Limited | Wholesale & retail | 2008 |
| Jubilee Court (Hounslow) Residents Association Limited | Households | 1994 |
| Judy Walker Associates Ltd | Professional & scientific | 2024 |
| Jules Chapman Makeup Limited | Professional & scientific | 2025 |
| Juniper Design Ltd | Professional & scientific | 2014 |
| Juno Strategic Ltd | Financial services | 2022 |
| Just a Minute Consulting Ltd | Professional & scientific | 2023 |
| Just Being Ollie Ltd | Professional & scientific | 2007 |
| Just Rowing Limited | Arts & recreation | 2001 |
| Justine Harris (Sardinia) Ltd | Real estate | 2021 |
| Juxposition Limited | Professional & scientific | 2014 |
| JW Netsolutions Ltd | Information & communication | 2018 |
| K.M.A & Associates Limited | Professional & scientific | 2023 |
| K.T. Quality Consulting Limited | Wholesale & retail | 2024 |
| KA Consultancy Partners Ltd | Professional & scientific | 2024 |
| Kalyana Aesthetics Ltd | Other services | 2024 |
| Kanso Analytics Ltd | Administrative & support | 2025 |
| Karen Davies Consulting Ltd | Professional & scientific | 2013 |
| Karen Levy Associates Limited | Health & social care | 2013 |
| Karmanline Limited | Information & communication | 2025 |
| Kasco Trading Ltd | Wholesale & retail | 1999 |
| Kays Cars Ltd | Administrative & support | 2025 |
| KBO Pictures Limited | Information & communication | 2017 |
| KE Events Consulting Ltd | Professional & scientific | 2025 |
| Kealy Farmar LLP | | 2008 |
| Kemble Mews Limited | Households | 2020 |
| Kenavon Drive Management Company Limited | Households | 1999 |
| Kench & Co Ltd | Professional & scientific | 2008 |
| Kenilworth Capital Limited | Real estate | 2023 |
| Kenton Theatre(Henley-On-Thames)Management Society Limited(The) | Arts & recreation | 1967 |
| Kepler Capital Limited | Administrative & support | 2019 |
| Kerb Property Limited | Real estate | 2016 |
| KGG Consulting Ltd | Professional & scientific | 2025 |
| Kidmore Place (Caversham) Management Company Limited | Households | 2008 |
| Kildridge Limited | Professional & scientific | 2020 |
| Kings Cross Road Limited | Households | 2004 |
| Kingswood Gate Management Company (Shiplake) Limited | Real estate | 1989 |
| Kingsworth Corporate Finance Limited | Professional & scientific | 2018 |
| Kingwood Windows Ltd | Wholesale & retail | 2019 |
| Kirschstein Designs Limited | Manufacturing | 2000 |
| Kitchen CUT Limited | Information & communication | 2011 |
| Kiya Survivors | Education | 2007 |
| Kizik Ltd | Hospitality | 2016 |