| ITM Integration Ltd | Information & communication | 2013 |
| ITM Property Investments Ltd | Real estate | 2023 |
| Itnw Ltd | Information & communication | 2023 |
| Iyana Limited | Information & communication | 2013 |
| J & D Bradbury Ltd | Real estate | 2017 |
| J & D Medical Ltd | Professional & scientific | 2018 |
| J & J Plastic Supplies Ltd | Other services | 2013 |
| J & J Windows & Doors Limited | Other services | 2011 |
| J a Wright Construction Ltd | Construction | 2020 |
| J C MAX Limited | Wholesale & retail | 2009 |
| J P Wealth Management Limited | Professional & scientific | 2016 |
| J&Gm Properties Limited | Real estate | 2018 |
| J&J Food and Events Ltd | Hospitality | 2024 |
| J'Ouvert Media Ltd | Administrative & support | 2026 |
| J.Demornay Ltd | Manufacturing | 2024 |
| J.K Real Planning Ltd | Construction | 2025 |
| J.K. Engineering (Sandy) Limited | Manufacturing | 2008 |
| J2G Consulting Limited | Information & communication | 2016 |
| Jabeso Privacy Solutions Limited | Professional & scientific | 2020 |
| JAC Architects Ltd | Professional & scientific | 2021 |
| Jackie Chapman Ltd | Education | 2025 |
| Jackson Mechanical Services (UK) Limited | Administrative & support | 2000 |
| Jacob Video Ltd | Information & communication | 2020 |
| Jakz Trading Ltd | Wholesale & retail | 2018 |
| James Ranch Properties Limited | Real estate | 2014 |
| James Stocks & Co Limited | Administrative & support | 2022 |
| James Worwood Ltd | Information & communication | 2021 |
| Jameson Court (ST Albans) Limited | Households | 2000 |
| Jamieson Locations Ltd | Arts & recreation | 2021 |
| Janine Tsoflias Limited | Information & communication | 2026 |
| Japan Links Limited | Wholesale & retail | 1989 |
| Jarvis Commercial Limited | Construction | 1945 |
| Jarvis Commercial Properties Limited | Real estate | 2000 |
| Jarvis Construction Limited | Construction | 1963 |
| Jarvis Group Construction Limited | Construction | 2011 |
| Jarvis Group Developments Limited | Construction | 2011 |
| Jarvis Group Limited | Construction | 2001 |
| Jarvis Harpenden Limited | Construction | 1946 |
| Jarvis Homes Limited | Construction | 1971 |
| Jarvis Indcom Limited | Real estate | 1984 |
| Jarvis Land (Strategic) Limited | Construction | 2024 |
| Jarvis Partnership Homes Limited | Construction | 2018 |
| Jasco (U.K.) Limited | Manufacturing | 1994 |
| JAY KAY Murphy Ltd | Construction | 2022 |
| JB Assets Limited | Real estate | 2014 |
| JB Leisure Consulting Ltd | Professional & scientific | 2021 |
| JBJ Studio Portobello Ltd | Information & communication | 2024 |
| JC Finance Consulting Ltd | Professional & scientific | 2016 |
| JC Tutoring Ltd | Education | 2025 |
| Jcavaree Interiors Ltd | Professional & scientific | 2022 |
| JCD Consulting Limited | Real estate | 2008 |
| JCO Consultants Limited | Professional & scientific | 2021 |
| JDH Music Limited | Wholesale & retail | 2018 |
| JDR Tech Ltd | Information & communication | 2025 |
| JE Film & Media Productions Ltd | Information & communication | 2025 |
| Jeavons Consulting Ltd | Professional & scientific | 2025 |
| Jelley's Meats Limited | Wholesale & retail | 2014 |
| Jenem Consultancy Limited | Administrative & support | 2022 |
| Jeremy Rance Consulting Services Limited | Administrative & support | 2010 |
| JES Marketing Limited | Professional & scientific | 2026 |
| Jessie Hosking Tennis Ltd | Education | 2026 |
| Jeton Digital Ltd | Wholesale & retail | 2020 |
| Jevington Logistics Limited | Other services | 1998 |
| Jevington Services (UK) Ltd | Other services | 2016 |
| JG Accord Limited | Administrative & support | 2024 |
| JG Business Services Limited | Administrative & support | 2024 |
| JGS Property Maintenance Ltd | Households | 2025 |
| JGS Trading Ltd | Construction | 2025 |
| JHT Property Limited | Information & communication | 2011 |
| Jigsaw Exchange Limited | Wholesale & retail | 2021 |
| Jimsom Limited | Wholesale & retail | 2024 |
| Jinwoo Property Services Limited | Construction | 2015 |
| JJ Locations Limited | Information & communication | 2026 |
| JKK Herts Ltd | Real estate | 2025 |
| JKS Assessments Limited | Public administration | 2017 |
| JL Pharma Consulting Limited | Professional & scientific | 2026 |
| JL25 Restaurants Ltd | Hospitality | 2025 |
| JLF Cosy Homes Ltd | Real estate | 2022 |
| JLM Architecture Limited | Professional & scientific | 2002 |
| JM Sweet Trading Limited | Wholesale & retail | 2011 |
| Jmmm Global Limited | Financial services | 2018 |
| JMS Access Hire Limited | Administrative & support | 2014 |
| Joanna Gilbert Art Limited | Arts & recreation | 2025 |
| Joanna Gilbert Prints Limited | Arts & recreation | 2025 |
| Joanna Scurlock Careers Consulting Ltd | Education | 2018 |
| Joans Jeans Ltd | Wholesale & retail | 2024 |
| John Hill Holdings Limited | Construction | 1958 |
| John Lamb Photography Limited | Professional & scientific | 2002 |
| John Liver Consulting Limited | Professional & scientific | 2022 |
| John Molson Ltd | Other services | 2003 |
| Jolantowo Ltd | Real estate | 2026 |
| Jonathan Taylor Publishing Consultancy Ltd | Information & communication | 2016 |
| Jord Media Ltd | Arts & recreation | 2025 |
| Josamid Ltd | Health & social care | 2022 |
| Jose Fertility Care Ltd | Health & social care | 2013 |
| Joseph Lewin Limited | Wholesale & retail | 2001 |
| Joubert Limited | Financial services | 2025 |
| JPR Group Ltd | Other services | 2015 |
| JPS GAS Ltd | Construction | 2015 |
| JSC (Stanhope Gardens) Ltd | Real estate | 2024 |