| J (Partners) Ltd. | Information & communication | 2002 |
| J C Productions Limited | Information & communication | 1999 |
| J. P. Cavill and SON Limited | Real estate | 1951 |
| J.C. Frost & Co. (Beaconsfield) Ltd | Real estate | 1990 |
| J.M.S.E. Holdings Limited | Real estate | 2017 |
| J.R. Tusting & Company Limited | Manufacturing | 1983 |
| JAC Property Consultants Limited | Professional & scientific | 2004 |
| Jackie Palmer Associates Limited | Arts & recreation | 2002 |
| Jackie Palmer Management Limited | Arts & recreation | 2002 |
| Jackson Property Consultancy Ltd | Professional & scientific | 2002 |
| Janssen-Cilag Limited | Manufacturing | 1971 |
| Japonica Management Company Limited | Households | 2001 |
| JC & J Properties Ltd | Real estate | 2024 |
| Jenkins Barn Limited | Real estate | 2022 |
| JGA Legal LLP | | 2007 |
| Jggj Limited | Information & communication | 2022 |
| JH Bonham & SON Limited | Agriculture & fishing | 2003 |
| JLM Services Limited | Other services | 2002 |
| John Carroll Consultancy Limited | Professional & scientific | 2012 |
| John Roughley & Associates | | 1988 |
| John Ruff Limited | Real estate | 1974 |
| John Whittenbury Financial Services Limited | Financial services | 1975 |
| John Williams (High Wycombe) Limited | Construction | 1941 |
| Johnson & Johnson Innovation Limited | Real estate | 2000 |
| Jordan Garden Services Limited | Administrative & support | 2003 |
| Josegarcia Ltd | Wholesale & retail | 2025 |
| KAI D Properties Limited | Real estate | 2015 |
| Kamold Ltd | Information & communication | 2006 |
| Kash-Uk Ltd | Wholesale & retail | 2025 |
| Kcabor Ltd | Information & communication | 2023 |
| Keeping Books Limited | Professional & scientific | 2002 |
| Kelmscot Building Co. Limited | Construction | 1955 |
| Kent Electrical Contracting Limited | Construction | 2011 |
| KEW Motors (Iver) Limited | Wholesale & retail | 2005 |
| Key Process and Solutions Limited | Information & communication | 2021 |
| Keyhole Data Limited | Information & communication | 1991 |
| Kfvo Ltd | Wholesale & retail | 2026 |
| Kilworth Marine Services Limited | Professional & scientific | 2006 |
| Kimble Estates Limited | Professional & scientific | 2002 |
| Kingsgate Associates Limited | Professional & scientific | 1988 |
| Kingswood Court Developments Limited | Construction | 2006 |
| KMD Services Ltd | Professional & scientific | 2003 |
| Kristall Clean Ltd | Administrative & support | 2019 |
| KTA Group Ltd. | Wholesale & retail | 1998 |
| KTM Inns Limited | Hospitality | 2007 |
| L B Woodmaster Ltd | Construction | 2016 |
| L3 Infotech Limited | Information & communication | 2023 |
| Langham Design & Build Limited | Professional & scientific | 2003 |
| Langley Property Company Limited | Real estate | 2003 |
| Lapwing Flying Group Limited | Arts & recreation | 1980 |
| Larvij International Limited | Wholesale & retail | 1991 |
| Lauderdale Mansions (South) Limited | Households | 1979 |
| Lawson Ware Limited | Administrative & support | 2003 |
| Lecter Holdings Limited | Financial services | 2022 |
| Leena Lakhani and Co | | 2004 |
| Leisure Matters (Robotsoccer) Limited | Arts & recreation | 2006 |
| LES Maisons Blanches Limited | Professional & scientific | 2002 |
| Lesrock Limited | Construction | 2005 |
| Letsmart Property Management Limited | Real estate | 2003 |
| Levanter Limited | Information & communication | 2004 |
| Linda Durtnal Associates Ltd | Professional & scientific | 2006 |
| Lion's Surprise Studio Limited | Wholesale & retail | 2025 |
| Llrm Ltd | Manufacturing | 2022 |
| Lochen Leather Limited | Extraterritorial | 2005 |
| London (UK) Chapter Rajasthan Foundation | Other services | 2026 |
| London Heating & Renewables Ltd | Construction | 2021 |
| London Side Products Limited | Extraterritorial | 1974 |
| Lords Estates Limited | Real estate | 1929 |
| Love Green Garage Limited | Wholesale & retail | 2003 |
| Lowther Battram Limited | Construction | 2005 |
| LSB Bathrooms Ltd | Construction | 2015 |
| Lumos Homes Four Limited | Real estate | 2023 |
| Luxor UK Limited | Professional & scientific | 2003 |
| Luxury Fever Limited | Wholesale & retail | 2006 |
| M.L. Boxall Limited | Construction | 1976 |
| Macken Music Limited | Information & communication | 2001 |
| Mackenzie Machinery Services Limited | Manufacturing | 2015 |
| Maclift Ltd. | Professional & scientific | 1984 |
| MAD Engineering Limited | Wholesale & retail | 2002 |
| Made by Machines Ltd | Arts & recreation | 2004 |
| Magnolia Court (the Village) Management Company Limited | Households | 2001 |
| Maharaj Distribution Limited | Professional & scientific | 2003 |
| Maitland Global Consulting Limited | Professional & scientific | 2007 |
| Makepeace Developments Limited | Professional & scientific | 2007 |
| Mando Corporation Limited | Financial services | 1977 |
| Mann Consulting Limited | Information & communication | 1998 |
| Manyplans Limited | Households | 1989 |
| Marchaven Homes Limited | Health & social care | 1986 |
| Marigold Cleaning Limited | Administrative & support | 2005 |
| Marketing Force (Services) Limited | Manufacturing | 2014 |
| Marlins Global Ltd | Wholesale & retail | 2015 |
| Marlow Tennis Club Limited | Arts & recreation | 2022 |
| Martin Enterprises Limited | Agriculture & fishing | 1981 |
| Martyn Services Limited | Financial services | 2003 |
| Maryam Pictures Ltd | Information & communication | 2017 |
| Mason Property Services Limited | Construction | 2004 |
| Matmobile Limited | Transport & logistics | 2012 |
| Maxim Communications Limited | Administrative & support | 1999 |
| MAY Saleh Limited | Professional & scientific | 2003 |
| Mayflower Associates Limited | Professional & scientific | 2006 |