| Irwell Solutions Limited | Information & communication | 2015 |
| It's Your Face Aesthetics Ltd | Health & social care | 2016 |
| J & M Landscapes Limited | Administrative & support | 2018 |
| J Allington Property Consultant Ltd | Professional & scientific | 2025 |
| J and B Garden Services Limited | Administrative & support | 2020 |
| J B Event Facilities Limited | Other services | 2007 |
| J G Pearson Heating & Plumbing Ltd | Construction | 2021 |
| J Levett GAS Services Limited | Construction | 2013 |
| J R Walker Ltd | Professional & scientific | 2003 |
| J&S Cycle Events Ltd | Arts & recreation | 2022 |
| J.A.Rundle(Oxford)Limited | | 1956 |
| J.W.Thomas & Sons(Farms)Limited | Agriculture & fishing | 1961 |
| JA Auto Electrical Ltd | Wholesale & retail | 2016 |
| JA Three Counties Property Consultants Limited | Real estate | 2025 |
| Jace Properties Limited | Real estate | 1989 |
| Jacques Forrest Capital Ltd | Real estate | 2020 |
| JAD Ward Construction Ltd | Construction | 2024 |
| Jade House Ltd | Hospitality | 2026 |
| James Lomax Ltd | Arts & recreation | 2023 |
| James Routledge Designs Ltd | Professional & scientific | 2019 |
| James Ward Films Limited | Professional & scientific | 2017 |
| Jamie B Ltd | Information & communication | 2024 |
| Jane & Peter Tinkler Limited | Professional & scientific | 2018 |
| Jarden Petcare Ltd | Professional & scientific | 2024 |
| Javelinas Group Limited | Administrative & support | 2013 |
| Jaxon Site Services Ltd | Administrative & support | 2025 |
| Jayjayc Limited | Manufacturing | 2026 |
| Jbrr Properties Limited | Real estate | 2023 |
| JC Countryside Ltd | Wholesale & retail | 2023 |
| JDE99 Ltd | Arts & recreation | 2025 |
| Jennah Music Limited | Arts & recreation | 2023 |
| Jerri Nagel Photography Ltd | Professional & scientific | 2023 |
| Jeskins Associates Limited | Professional & scientific | 2011 |
| JET FLO Pro UK Ltd | Administrative & support | 2021 |
| JJ Electix Limited | Construction | 2016 |
| Jjhf Investment Holdings Ltd | Financial services | 2025 |
| JJL Design Limited | Wholesale & retail | 2025 |
| JK Automotive Training Solutions Limited | Education | 2022 |
| JL Garage Ltd | Wholesale & retail | 2019 |
| Jmsgc Ltd | Professional & scientific | 2022 |
| Jobling Property Ltd | Real estate | 2023 |
| John's Garage Ltd | Wholesale & retail | 2024 |
| Jolt & Partners Limited | Professional & scientific | 2020 |
| Joshua Arne Rowland Ltd | Wholesale & retail | 2023 |
| Joshua Valentine Associates Ltd | Professional & scientific | 2019 |
| JPR Competition Ltd | Manufacturing | 2017 |
| Jryoung Ltd | Arts & recreation | 2023 |
| JS Media Associates Limited | Professional & scientific | 2012 |
| JTB Autos Ltd | Wholesale & retail | 2021 |
| Jubilee Barn Limited | Agriculture & fishing | 2015 |
| Jubilee Construction Management Service Limited | Construction | 2016 |
| Junefield Associates Limited | Professional & scientific | 2014 |
| Juno Marketing Consultancy Ltd | Professional & scientific | 2024 |
| JW XT Ltd | Financial services | 2020 |
| K & D Flooring Ltd | Construction | 2022 |
| K Grantham Ltd | Hospitality | 2025 |
| K&M Bosson Company Limited | Professional & scientific | 2023 |
| Kaizen 3 Consulting Ltd | Professional & scientific | 2025 |
| Kate Gibbs Consulting Limited | Professional & scientific | 2013 |
| KB Weld Fabrications Ltd | Manufacturing | 2026 |
| Keep Biking Limited | Real estate | 1998 |
| Keith Watts Ltd | Information & communication | 2020 |
| Kelly Fogden Ltd | Administrative & support | 2020 |
| Kelmore Grove Limited | Households | 1999 |
| Kendrew T Limited | Wholesale & retail | 2011 |
| Kenpark Investments Ltd | Real estate | 2011 |
| Khushboo (Brackley) Ltd | Hospitality | 2015 |
| KIM Viet Travel Ltd | Administrative & support | 2022 |
| Kirsty Parsons Properties Ltd | Real estate | 2025 |
| KLE Plastic Products Limited | Manufacturing | 2018 |
| KM Healthcare Consulting Ltd | Professional & scientific | 2019 |
| KME Machinery Limited | Financial services | 2023 |
| Kmhr Solutions Limited | Professional & scientific | 2015 |
| KMS Aviation Services Limited | Administrative & support | 2025 |
| Knight Cleaning Services Limited | Administrative & support | 2011 |
| Koflach Engineering Ltd | Professional & scientific | 2024 |
| KPH Tyres & Motor Repairs (Farthinghoe) Limited | Wholesale & retail | 2021 |
| KPM Civil Engineering Limited | Construction | 2025 |
| KPM Contracting Limited | Construction | 2021 |
| KPS Tree & Ground Care Limited | Administrative & support | 2024 |
| Kwikbleed Limited | Professional & scientific | 2025 |
| L & G Ventures Limited | Professional & scientific | 2011 |
| L J Rothwell Limited | Administrative & support | 2015 |
| L Muir Holdings Limited | Professional & scientific | 2018 |
| Lamda Engineering Services Limited | Manufacturing | 2012 |
| Lane Bookkeeping & Accounting Ltd | Professional & scientific | 2008 |
| Lane END Construction Services Ltd | Professional & scientific | 2021 |
| Larpent Newton & Company Limited | Professional & scientific | 1977 |
| Larpent Newton Holdings Limited | Professional & scientific | 1988 |
| Laundryquip LLP | | 2003 |
| Laura Crompton Ltd | Health & social care | 2024 |
| Lawkan Construction Ltd | Construction | 2018 |
| Lawnatics Limited | Agriculture & fishing | 2006 |
| Lawrence Furnishings Limited | Wholesale & retail | 2010 |
| LB Realty Limited | Real estate | 2018 |
| LC Autos Limited | Wholesale & retail | 2012 |
| LC Autos Recycling Limited | Professional & scientific | 2016 |
| Leap Consultancy Limited | Extraterritorial | 2016 |
| Lebanese Grill MK Limited | Hospitality | 2026 |
| LEM 77 Group Limited | Financial services | 2024 |