| J M Electrical LDN Ltd | Construction | 2022 |
| J P a Consulting Limited | Information & communication | 1998 |
| J Patterson Holdings Limited | Financial services | 2022 |
| J S ALL Solutions Ltd | Construction | 2014 |
| J S Baker Carpentry & Kitchens Ltd | Construction | 2015 |
| J Sparks Electrical Ltd | Energy | 2017 |
| J Spooner Groundworks & Demolition Limited | Construction | 2018 |
| J U Events Ltd | Hospitality | 2021 |
| J White Electrical Limited | Construction | 2020 |
| J Wright Investment Management Ltd | Financial services | 2018 |
| J&H Multi Limited | Wholesale & retail | 2020 |
| J&J Build Solutions Ltd | Construction | 2023 |
| J&J Building Solution Ltd | Construction | 2021 |
| J&J Flooring Services Ltd | Construction | 2025 |
| J&J World Construction Ltd | Construction | 2026 |
| J&K Electrical Services Ltd | Construction | 2023 |
| J&M Wilson Holdings Limited | Financial services | 2026 |
| J&S Consulting Ltd | Professional & scientific | 2018 |
| J&S Okani Ltd | Health & social care | 2025 |
| J&T Window Cleaning Services Ltd | Administrative & support | 2017 |
| J-Mech Waste Solutions Ltd | Construction | 2021 |
| J. MA BMS Commissioning Services Ltd. | Construction | 2009 |
| J.A.S & a Investment Limited | Real estate | 2024 |
| J.C.C. Engineering Limited | Construction | 1995 |
| J.D 37 Ltd | Transport & logistics | 2013 |
| J.E.J KEH Limited | Health & social care | 2015 |
| J.K Clearance Ltd | Water & waste | 2026 |
| J2 Commercial Flooring Ltd | Construction | 2026 |
| J2 Floors & Walls Ltd | Construction | 2026 |
| J37 Enterprises Ltd | Information & communication | 2023 |
| J7INTERIORS Ltd | Construction | 2023 |
| Jaaas Real Estate Limited | Real estate | 2021 |
| Jaade Limited | Households | 2025 |
| Jabbie Property Holdings Ltd | Real estate | 2025 |
| JAC Cleaning Limited | Administrative & support | 2014 |
| Jace Wines Limited | Wholesale & retail | 2019 |
| Jackdaw Antiques Limited | Extraterritorial | 2012 |
| Jacob Ladders Ltd | Construction | 2017 |
| Jacob White and Company Limited | Manufacturing | 2005 |
| Jacob,White(Packaging)Limited | Manufacturing | 1971 |
| Jada Homes Ltd | Real estate | 2024 |
| Jade’S Laser Solutions Ltd | Other services | 2020 |
| Jadonjan Ltd | Health & social care | 2020 |
| Jaga Real Estate Ltd | Real estate | 2024 |
| Jaguar Plumbing Ltd | Construction | 2022 |
| Jaguillon Ltd | Health & social care | 2019 |
| JAI Tech Ltd | Information & communication | 2019 |
| Jaitly Trading Co Ltd | Wholesale & retail | 2008 |
| Jaivaarahi Limited | Real estate | 2026 |
| Jaliban Ltd | Wholesale & retail | 2020 |
| Jallcock Coaching Limited | Education | 2024 |
| Jaltarang Limited | Other services | 2022 |
| JAM Electrical Services Ltd. | Construction | 2003 |
| James Bishop Golf Services Ltd. | Wholesale & retail | 2013 |
| James Black Coaching Ltd | Arts & recreation | 2026 |
| James Carney Architects Limited | Professional & scientific | 2015 |
| James Graham Transport (Kent) Limited | Extraterritorial | 1973 |
| James Grist Photography Ltd | Professional & scientific | 2025 |
| James R. Cain Ltd | Manufacturing | 2015 |
| James Steel Solutions Ltd | Manufacturing | 2026 |
| Jameson Carter Ltd | Wholesale & retail | 2001 |
| Jana Construction Limited | Construction | 2021 |
| Jana's Design & Creations Ltd | Professional & scientific | 2018 |
| Janca Kent Homes Ltd | Construction | 2023 |
| Jane James's Consultancy Limited | Administrative & support | 2013 |
| Janet Ltd | Extraterritorial | 2006 |
| Janetgold Hair and Wigs Limited | Other services | 2020 |
| Janette Jackson Ltd | Health & social care | 2014 |
| Janice Hennessy Limited | Education | 2009 |
| Janus Management Services Ltd | Administrative & support | 2016 |
| Janza Ltd | Real estate | 2024 |
| Japurk Ltd | Other services | 2020 |
| Jarbb Ltd | Information & communication | 2023 |
| Jarbhub Ltd | Administrative & support | 2026 |
| Jaron Ltd | Professional & scientific | 2013 |
| Jarvis Blake Limited | Administrative & support | 2003 |
| Jask Associates Limited | Health & social care | 2022 |
| Jasney Limited | Manufacturing | 2023 |
| Jason Logistics Limited | Transport & logistics | 2025 |
| Jasper Granite & Jasper Sales Recruitment Ltd | Administrative & support | 2024 |
| JAT Control Services Ltd | Construction | 2023 |
| JAT Markets Ltd | Other services | 2024 |
| JAX Bayswater Ltd | Real estate | 2024 |
| JAY & Mich Ltd | Real estate | 2022 |
| JAY Ashley Cars Limited | Wholesale & retail | 2026 |
| JAY Gavin Trade Sales Ltd | Wholesale & retail | 2025 |
| JAY Logistic International Limited | Transport & logistics | 2018 |
| Jay's Carpet Cleaning Limited | Administrative & support | 2019 |
| Jay-Beetee Healthcare Ltd | Health & social care | 2025 |
| Jaya Finexpert Services Limited | Real estate | 2021 |
| Jaychiz Services Ltd | Professional & scientific | 2018 |
| Jays Car Detailing Ltd | Wholesale & retail | 2024 |
| Jays Carpentry Limited | Construction | 2010 |
| Jayvic Consulting Limited | Administrative & support | 2017 |
| JB Construction & Renovations Ltd | Construction | 2023 |
| JB Diamond Drilling & Sawing Limited | Construction | 2016 |
| JB Soft Ltd | Information & communication | 2016 |
| JB5 Trading Ltd | Real estate | 2024 |
| JBA Compliance Consultancy Limited | Professional & scientific | 2025 |
| Jbhd Services Limited | Administrative & support | 2025 |