| JGS Group Ltd | Financial services | 2019 |
| JH Research Consulting Limited | Professional & scientific | 2018 |
| Jhanson Ltd | Wholesale & retail | 2025 |
| Jigsaw Education Group Limited | Education | 2021 |
| Jigsaw Education Limited | Education | 2013 |
| Jigsaw Pshe Ltd | Education | 2023 |
| Jimmyswrld Ltd | Professional & scientific | 2024 |
| JJ Tilley Limited | Construction | 2010 |
| JJM UK Investments Limited | Real estate | 2022 |
| Jkey.Tech Limited | Arts & recreation | 2018 |
| JL Controls Limited | Construction | 2019 |
| JL Elite Coaching Ltd | Education | 2026 |
| JLA Insights Limited | Information & communication | 2025 |
| JLA Tech Limited | Information & communication | 2017 |
| JLM Logistics Ltd | Transport & logistics | 2025 |
| JLM Plumbing and Heating Services Ltd | Construction | 2022 |
| JM Transformers Limited | Manufacturing | 2003 |
| JMD Groundwork Solutions Limited | Construction | 2023 |
| JMD Property Developments (Surrey) Ltd | Construction | 2024 |
| JMS Design and Construction Ltd | Construction | 2017 |
| JMS Drinks (Holdings) Limited | Professional & scientific | 2007 |
| JMS Drinks Limited | Manufacturing | 2006 |
| JND Landscaping Limited | Administrative & support | 2017 |
| Jocelyn Pook Limited | Information & communication | 2002 |
| Jodan Properties UK Limited | Financial services | 2023 |
| Jofra Archer Limited | Wholesale & retail | 2019 |
| John Jenkins Locksmiths Limited | Administrative & support | 2016 |
| John Stanley Ltd | Wholesale & retail | 2020 |
| Johns Close 1966 Limited | Extraterritorial | 2014 |
| Joint Audio Media Education Services Ltd | Education | 2006 |
| JON Collins Engineering Services Limited | Professional & scientific | 2023 |
| Jonat Trading Ltd | Wholesale & retail | 2019 |
| Jonathan Ashdown Ltd | Information & communication | 2016 |
| Joni Food Ltd | Hospitality | 2023 |
| Joseph DMS Holdings Limited | Financial services | 2020 |
| Josh Brown Consultancy Limited | Professional & scientific | 2025 |
| Josh Dominguez Limited | Professional & scientific | 2014 |
| Joshua Coppen Ltd | Professional & scientific | 2024 |
| Jouberttraining Ltd | Arts & recreation | 2025 |
| Jpal Consulting Ltd | Professional & scientific | 2024 |
| JPC Retail Limited | Wholesale & retail | 2024 |
| Jpelevate.Io Ltd | Professional & scientific | 2025 |
| JPK Consultants Ltd | Other services | 2007 |
| JPM Systems Limited | Information & communication | 2019 |
| JPS Accountancy Limited | Professional & scientific | 2017 |
| JR Childs & SON Limited | Other services | 2023 |
| JSR Research Ltd | Construction | 2023 |
| JSY Construction Ltd | Construction | 2018 |
| Jtbh LLP | | 2012 |
| JTR Technica Ltd | Wholesale & retail | 2023 |
| Jules Thin Crust UK Ltd. | Construction | 2015 |
| Julian Pindar Luthierie Ltd | Wholesale & retail | 2020 |
| Julie West Solicitors Ltd | Professional & scientific | 2020 |
| Junction 9 Media Services Ltd. | Information & communication | 2010 |
| Juniper Shores Limited | Administrative & support | 2019 |
| Just Beyond Ordinary Ltd | Professional & scientific | 2022 |
| Just Pads Ltd | Wholesale & retail | 2018 |
| Justin Clarke Accounting Services Limited | Professional & scientific | 2016 |
| Justin Rodriguez Services Limited | Administrative & support | 2013 |
| Justminded Limited | Health & social care | 2021 |
| JVG & Associates Limited | Professional & scientific | 2018 |
| JWD People Solutions Limited | Administrative & support | 2017 |
| K B S Properties Limited | Real estate | 2010 |
| K S Sehgal Services Limited | Professional & scientific | 2016 |
| Kable Recruitment Ltd | Administrative & support | 2024 |
| Kadarabrite Limited | Education | 2016 |
| Kalbay Limited | Hospitality | 2024 |
| Kama Consulting Limited | Professional & scientific | 2025 |
| Kama Holdings Limited | Wholesale & retail | 2024 |
| Kama Property Solutions Limited | Real estate | 2024 |
| Kamalaa Limited | Wholesale & retail | 2025 |
| Kamil the Builder Ltd | Construction | 2016 |
| Kanonkop Ltd | Financial services | 2013 |
| Kaobido Ltd | Health & social care | 2026 |
| KAP Properties Group Limited | Real estate | 2025 |
| Karma Management Limited | Households | 1998 |
| KAS Property Solutions Limited | Real estate | 2021 |
| Kate O'Connor Consulting Limited | Professional & scientific | 2014 |
| Kati Kaia Ltd | Wholesale & retail | 2018 |
| Katie Kloska Ltd | Health & social care | 2015 |
| Katie White Marketing Consulting Ltd | Information & communication | 2023 |
| Kaufman Consulting Ltd | Professional & scientific | 2024 |
| Kawamura Clapham Limited | Hospitality | 2022 |
| Kaya Consultancy Limited | Professional & scientific | 2013 |
| Kaya Films Limited | Information & communication | 2013 |
| Kayangan Holdings Limited | Real estate | 2024 |
| KBR (Aspire Construction Ventures) Holdings Limited | Financial services | 2018 |
| KBR (Aspire Construction Ventures) Holdings NO. 2 Limited | Financial services | 2018 |
| KBR (Aspire Construction Ventures) Limited | Construction | 2018 |
| KBR (Aspire Construction) Holdings Limited | Financial services | 2006 |
| KBR (Aspire Construction) Holdings NO.2 Limited | Financial services | 2006 |
| KBR (Aspire Construction) Limited | Other services | 2006 |
| KBR (Aspire Services Ventures) Holdings Limited | Financial services | 2018 |
| KBR (Aspire Services Ventures) Holdings NO. 2 Limited | Financial services | 2018 |
| KBR (Aspire Services Ventures) Limited | Administrative & support | 2018 |
| KBR (Aspire Services) Holdings Limited | Financial services | 2006 |
| KBR (Aspire Services) Holdings NO. 2 Limited | Financial services | 2006 |
| KBR (Aspire Services) Limited | Other services | 2006 |
| KBR (I) Limited | Professional & scientific | 2016 |
| KBR (U.K.) Investments Limited | Financial services | 2011 |