| Jnpj Holdings Limited | Financial services | 2026 |
| JO Painter Design Ltd | Arts & recreation | 2024 |
| JO Thompson Recruitment Limited | Administrative & support | 2003 |
| Joanna Graham Ecology Ltd | Professional & scientific | 2024 |
| Joanna Griffin Limited | Health & social care | 2012 |
| Joat Limited Partnership | | 1994 |
| Jodie Services Ltd | Wholesale & retail | 2013 |
| Joe's Fruit and VEG Limited | Wholesale & retail | 2026 |
| John Davies Dental Laboratory Limited | Health & social care | 2007 |
| John J Campbell Limited | Hospitality | 2010 |
| John Liddiard Farms Limited | Agriculture & fishing | 1978 |
| John Matthews Physio Ltd | Health & social care | 2010 |
| John Miranda Transport Ltd | Transport & logistics | 2022 |
| John Points Consulting Limited | Professional & scientific | 2014 |
| John Stean & Sons Limited | Professional & scientific | 1999 |
| John Traill Limited | Other services | 2013 |
| Johnson Associates Consultancy Ltd | Professional & scientific | 2010 |
| Johnsons (Henley) Limited | Administrative & support | 1934 |
| Johnston Parke Interiors Limited | Professional & scientific | 2009 |
| Joint Space Limited | Other services | 2019 |
| Jomy Limited | Education | 2020 |
| JON Curtis Solutions Ltd | Information & communication | 2017 |
| Jones Holidays Limited | Administrative & support | 2011 |
| Jonjo O'Neill Racing Limited | Extraterritorial | 2024 |
| Jorion Ltd | Real estate | 2012 |
| Joseph Mathew and Co Ltd | Information & communication | 2023 |
| Journey Clothing Co. Ltd | Extraterritorial | 2024 |
| Journey Digital Emea Limited | Information & communication | 2021 |
| Joycewords Ltd | Information & communication | 2013 |
| JPD Contracts (UK) Limited | Extraterritorial | 2005 |
| JPD Contracts Holdings Limited | Extraterritorial | 2014 |
| JPE Hris Consulting Limited | Other services | 2018 |
| Jpml Ltd | Arts & recreation | 2015 |
| JPS Safety and Engineering Ltd | Professional & scientific | 2020 |
| Jrlay Ltd | Education | 2022 |
| JRM Brokers Limited | Real estate | 2020 |
| JRM Property Holdings Limited | Real estate | 2020 |
| JRP Property Rental Limited | Real estate | 2022 |
| JTL Systems Limited | Manufacturing | 1985 |
| Jubilee Court (Thatcham) RMC Limited | Households | 2021 |
| Julaarth Limited | Education | 2025 |
| Julia Polish Food Ltd | Wholesale & retail | 2016 |
| Julian Hendey Ltd | Professional & scientific | 2020 |
| Julian Stokes Management Limited | Professional & scientific | 2005 |
| Jumblebee Ltd | Other services | 2010 |
| Jump-In-Uk Limited | Arts & recreation | 2021 |
| JUMP2IT Ltd | Arts & recreation | 2022 |
| JUMP4YOU Ltd | Arts & recreation | 2020 |
| Junction Road Croydon Limited | Real estate | 2015 |
| Juniper Dogs Ltd | Administrative & support | 2023 |
| Juno Consultancy Limited | Professional & scientific | 2006 |
| Junonia Advisory Limited | Administrative & support | 2023 |
| Just IFA Limited | Financial services | 2010 |
| JWA Race Engineering Limited | Wholesale & retail | 2013 |
| JWC Academy Ltd. | Administrative & support | 2005 |
| K & B Fletcher Limited | Wholesale & retail | 1980 |
| K and J Pubs Limited | Hospitality | 2025 |
| K J Herbert Limited | Other services | 2002 |
| K Supplies Holdings Limited | Extraterritorial | 2006 |
| K Supplies Limited | Extraterritorial | 1988 |
| K&G Scientific Authoring Limited | Professional & scientific | 2016 |
| K&J Brothers Ltd | Transport & logistics | 2023 |
| K.Point (Newbury) Management Company Limited | Households | 2004 |
| K8TE Signature Ltd | Other services | 2026 |
| KAI Carter Estates Limited | Real estate | 2019 |
| Kaibe Limited | Information & communication | 2017 |
| Kaiya AI Ltd | Information & communication | 2024 |
| Kalcie Ltd | Other services | 2023 |
| Kalculo Ltd | Professional & scientific | 2024 |
| Kalios Technologies Limited | Other services | 2023 |
| Kamba Limited | Information & communication | 2007 |
| KANREVI5 IT Consultancy Ltd | Information & communication | 2017 |
| Kansys International Ltd | Information & communication | 2019 |
| Kard Group Limited | Real estate | 2020 |
| KAS (Newbury) Limited | Other services | 2003 |
| Kaskada Ltd | Professional & scientific | 2018 |
| Kaskela Investments Limited | Administrative & support | 2005 |
| Kate Talbot Financial Planning Limited | Financial services | 2021 |
| Katelyst Consulting Ltd | Professional & scientific | 2012 |
| Katies Beauty Ltd | Other services | 2011 |
| Kaya Alpacas Ltd | Agriculture & fishing | 2025 |
| KC2 Networks Limited | Information & communication | 2012 |
| KCP Construction Limited | Construction | 2004 |
| KDG Solutions Limited | Wholesale & retail | 2025 |
| Kebekier Limited | Wholesale & retail | 2008 |
| Keen Newport Group Ltd. | Wholesale & retail | 2021 |
| Keith Ltd | Extraterritorial | 2016 |
| Keldisk Limited | Extraterritorial | 1996 |
| Kelly Rai’S Hair Studio Limited | Other services | 2022 |
| Kelly's Aerial Academy Ltd | Education | 2025 |
| Kemp BIZ Analysis Services Ltd | Information & communication | 2018 |
| Kempen Horticultural Services UK Ltd | Agriculture & fishing | 2016 |
| Kempsford Capital Ltd | Financial services | 2025 |
| Kempshott Car Sales Limited | Wholesale & retail | 2012 |
| Kempton Driving Instructors Limited | Education | 2021 |
| Kenmasco Limited | Administrative & support | 2006 |
| Kenmore Properties Limited | Real estate | 1935 |
| Kennedy Worx Limited | Other services | 2019 |
| Kennet Community Radio | Information & communication | 2012 |
| Kennet DAB Limited | Information & communication | 2025 |