| J.F. Associates Organisation Limited | Other services | 2006 |
| J.Haakmat Limited | Administrative & support | 2012 |
| J.L. Ashby & Company Limited | Agriculture & fishing | 1942 |
| J.M. Turner Brickwork Limited | Construction | 2008 |
| J.P.C. (Interiors) Limited | Construction | 1987 |
| J.R. Marriott (Collingham) Limited | Transport & logistics | 1951 |
| J.R. Wittey (Holdings) Limited | Professional & scientific | 1986 |
| J.Salmon & Partners Ltd | Agriculture & fishing | 2015 |
| J.Stenas Ltd | Transport & logistics | 2015 |
| J1B Consultants Limited | Wholesale & retail | 2023 |
| J21 Investments Ltd | Real estate | 2022 |
| J2L Integrated Care and Support Ltd | Administrative & support | 2022 |
| J3DSTUDIO Limited | Extraterritorial | 2025 |
| J4 Developments Limited | Hospitality | 2001 |
| J4G Limited | Other services | 2019 |
| J8 Property Investments Ltd | Real estate | 2021 |
| JA Savill Consulting Limited | Information & communication | 2009 |
| Jaabconnect Ltd | Information & communication | 2025 |
| Jaad Consulting Ltd | Health & social care | 2021 |
| Jaan Learning & Development Ltd | Professional & scientific | 2011 |
| Jaba Construct Limited | Administrative & support | 2024 |
| Jabacare Limited | Health & social care | 2021 |
| Jabez Trading Limited | Professional & scientific | 2019 |
| JAC Surveyors Limited | Professional & scientific | 2024 |
| Jacaranda Assets Ltd | Real estate | 2025 |
| Jack Flames Ltd | Public administration | 2018 |
| Jack Tree Greens Ltd | Real estate | 2022 |
| Jack's Fishbar Spalding Limited | Wholesale & retail | 2005 |
| Jackdaclipper Ltd | Other services | 2026 |
| Jackdaw Executive Coaching and Consultancy Ltd | Professional & scientific | 2020 |
| Jackie's Creations and Designs Ltd | Professional & scientific | 2019 |
| Jacks LAB Limited | Professional & scientific | 2021 |
| Jacks OR Better Limited | Administrative & support | 2020 |
| Jackson Pubs Limited | Hospitality | 2017 |
| Jacobson Chemicals Limited | Wholesale & retail | 1978 |
| Jacobson Space Limited | Other services | 2009 |
| Jacop Cars Ltd | Wholesale & retail | 2025 |
| Jacqueline Paula Brooks Limited | Extraterritorial | 2022 |
| Jacqueline Paula Wright Limited | Extraterritorial | 2021 |
| Jacquilyne's Ltd | Health & social care | 2017 |
| Jacv Limited | Hospitality | 2018 |
| Jada Consult Ltd | Information & communication | 2019 |
| Jadara Pharma Limited | Professional & scientific | 2005 |
| Jade Electrics Ltd | Construction | 2025 |
| Jade Hoses & Accessories Limited | Wholesale & retail | 2014 |
| Jade Trade Limited | Wholesale & retail | 2026 |
| Jade Tyres LLP | | 2012 |
| Jadeite Properties Limited | Real estate | 2025 |
| Jades Catering Services Ltd | Hospitality | 2018 |
| Jadr Portfolio & Asset Mgmt Ltd | Real estate | 2017 |
| Jadson Business Ltd | Health & social care | 2019 |
| Jaffair Limited | Manufacturing | 2004 |
| Jaffer Holdings Ltd | Real estate | 2016 |
| Jaffer Pharma Services Ltd | Wholesale & retail | 2018 |
| Jaffer Stroud Holdings Limited | Administrative & support | 2018 |
| Jaffs Restaurants Ltd | Hospitality | 2016 |
| JAG London Ltd | Wholesale & retail | 2017 |
| JAG Marketing Ltd | Professional & scientific | 2008 |
| JAG Simply Cleaning Ltd | Administrative & support | 2021 |
| Jagana Investments Limited | Real estate | 2017 |
| Jagl Ltd | Real estate | 2019 |
| Jagne Medi-K Ltd | Health & social care | 2013 |
| Jago Partners (London) Limited | Administrative & support | 2011 |
| Jags Consulting Limited | Professional & scientific | 2017 |
| Jaguars Rugby Academy Ltd | Education | 2024 |
| Jai-Sanitix Limited | Administrative & support | 2021 |
| Jaijia Investments Limited | Real estate | 2018 |
| Jain & Morris Ltd | Administrative & support | 2021 |
| JAK Design Limited | Professional & scientific | 2004 |
| Jakaranda Limited | Households | 2006 |
| Jake CAN Make: Custom Creations Ltd | Manufacturing | 2022 |
| Jakh Ltd | Arts & recreation | 2012 |
| Jaktek Ltd | Professional & scientific | 2020 |
| Jal-Industrial Limited | Hospitality | 2022 |
| Jalex Futures Ltd | Financial services | 2015 |
| Jalex SPV1 Limited | Professional & scientific | 2023 |
| Jalex SPV2 Limited | Professional & scientific | 2023 |
| Jalex SPV3 Limited | Professional & scientific | 2023 |
| Jallandars Ltd | Wholesale & retail | 2021 |
| Jam's Breakdown and Recovery Ltd | Transport & logistics | 2026 |
| Jam's Traders MK Limited | Wholesale & retail | 2025 |
| Jama Works Ltd | Wholesale & retail | 2025 |
| Jambo Auto Trading Ltd | Wholesale & retail | 2025 |
| Jambo Logistics Ltd | Wholesale & retail | 2010 |
| James Branson Limited | Wholesale & retail | 2020 |
| James Brown Industries Limited | Manufacturing | 2004 |
| James Conveyancing Limited | Professional & scientific | 2020 |
| James Darling Limited | Professional & scientific | 2017 |
| James KAY Architects Limited | Professional & scientific | 2015 |
| James Mark Consulting Limited | Professional & scientific | 2013 |
| James Murphy Services Limited | Construction | 2025 |
| James Peat Limited | Professional & scientific | 2022 |
| James Seymour Property Group Ltd | Households | 2026 |
| James Smythe Limited | Arts & recreation | 2023 |
| James Titus Ltd | Real estate | 2022 |
| JAMES100 Ltd | Other services | 2018 |
| Jamf Ltd | Information & communication | 2012 |
| Jamf Software UK Limited | Information & communication | 2013 |
| Jamie Rickell Carpentry Limited | Construction | 2017 |
| Jamie's Carpets Limited | Construction | 2015 |