| International Flow Battery Forum Limited | Administrative & support | 2022 |
| Intuitionuk Ltd | Information & communication | 2007 |
| Investment Group Bath Ltd | Administrative & support | 2024 |
| Investorgaters Limited | Information & communication | 2012 |
| Investy Limited | Construction | 1979 |
| Invisible Sky UK Holdings Ltd | Real estate | 2023 |
| Invoice Finance Connect Limited | Other services | 2016 |
| IOS Company UK Limited | Professional & scientific | 2009 |
| IP Holdings Ltd | Financial services | 2023 |
| Iplumb Wilts Ltd. | Extraterritorial | 2013 |
| IPM Global Services Limited | Professional & scientific | 2023 |
| Ipno Ltd | Other services | 2024 |
| IRB Financial Services Limited | Financial services | 2003 |
| IRECRUIT4 Ltd | Administrative & support | 2021 |
| Ironbright Homes Limited | Real estate | 2016 |
| IS Commercial Ltd. | Professional & scientific | 2026 |
| Is-Tech Software and Technology Solutions Ltd | Information & communication | 2017 |
| Isabel Grace Interiors Ltd | Professional & scientific | 2016 |
| Isla Nublar Limited | Financial services | 2019 |
| Isocom (Bristol) Limited | Administrative & support | 2017 |
| Isometric Systems Ltd | Administrative & support | 2024 |
| Issin Tech Ltd | Information & communication | 2022 |
| Itek Colour Graphics Limited | Information & communication | 2002 |
| ITT Interiors Ltd | Wholesale & retail | 2023 |
| Ives Decorating Services Ltd | Construction | 2019 |
| IVY Renovations Limited | Financial services | 2025 |
| Ixys UK Westcode Ltd. | Manufacturing | 1997 |
| J & L Hospitality Limited | Hospitality | 2012 |
| J & L Retail Limited | Administrative & support | 2016 |
| J & M Bodman Limited | Administrative & support | 2007 |
| J & M Developments SW Ltd | Construction | 2025 |
| J & R Collingborn Ltd | Agriculture & fishing | 2007 |
| J a Plant and Groundworks Limited | Construction | 2016 |
| J C Autos (Chippenham) Limited | Wholesale & retail | 2018 |
| J D Wright & SON Ltd | Agriculture & fishing | 2009 |
| J Deeprose Developments Ltd | Construction | 2019 |
| J E Mitchell Ltd | Construction | 2021 |
| J F Harrison Limited | Information & communication | 2015 |
| J Forster Property Services Ltd | Real estate | 2025 |
| J J Payne & SON Limited | Agriculture & fishing | 2017 |
| J J Siga Limited | Construction | 2004 |
| J L Hall Ltd | Professional & scientific | 2006 |
| J M Brunt Livestock Limited | Transport & logistics | 2014 |
| J Prangle Ltd | Energy | 2009 |
| J R Conway Engineering Limited | Professional & scientific | 2009 |
| J S N Hbros Limited | Administrative & support | 2012 |
| J Sheppard and SON Limited | Construction | 2013 |
| J T Webb Ltd | Transport & logistics | 2021 |
| J W Swales & Co Limited | Professional & scientific | 1999 |
| J&A Property Investment Group Ltd | Construction | 2025 |
| J&L Winterbourne Ltd | Hospitality | 2019 |
| J&R Shanks Ltd | Administrative & support | 2022 |
| J. Rouse & SON Limited | Wholesale & retail | 1975 |
| J.A. Wicks and Sons Limited | Construction | 1972 |
| J.A.Edwards Insurance Brokers Limited | Financial services | 2023 |
| J.Ad Estates Ltd | Real estate | 2025 |
| J.C. Hare Limited | Wholesale & retail | 1959 |
| J.D.Sweet Limited | Construction | 2022 |
| J.W. Groundworks Limited | Construction | 2012 |
| J13 Consulting Ltd | Professional & scientific | 2023 |
| Jabs Holdings Ltd | Real estate | 2025 |
| Jack Coathupe Media Limited | Professional & scientific | 2023 |
| Jack Humphrys Builders Ltd | Construction | 2017 |
| Jack Roberts Services Ltd | Construction | 2015 |
| Jackson & Daughters Holdings Ltd | Professional & scientific | 2023 |
| Jadaha Investments Ltd | Real estate | 2021 |
| JAE Programme Management Ltd | Professional & scientific | 2023 |
| JAM Music Group Limited | Arts & recreation | 2021 |
| JAM Productions Group Limited | Information & communication | 2023 |
| James Burton Property Ltd | Real estate | 2017 |
| James Currie Engineering Services Limited | Construction | 2007 |
| James D Digital Limited | Information & communication | 2017 |
| James Gwinnett Ltd | Professional & scientific | 2025 |
| James Hutchings Limited | Agriculture & fishing | 2005 |
| James Interior Design Ltd | Construction | 2024 |
| James Morris Limited | Administrative & support | 2019 |
| James Properties (Wiltshire) Limited | Real estate | 2016 |
| Jamie Cabral Trading Ltd | Financial services | 2025 |
| Jamy Limited | Manufacturing | 1982 |
| Jane James and Associates Limited | Administrative & support | 2010 |
| Janik and Shaw Limited | Wholesale & retail | 2016 |
| Janner Properties Limited | Real estate | 2025 |
| Janus Property Assets Limited | Real estate | 2017 |
| Jarvis Transport (YK) Limited | Transport & logistics | 2014 |
| JAS Property Services Limited | Other services | 2016 |
| Javelin Solutions Limited | Information & communication | 1997 |
| JAX Dance Limited | Arts & recreation | 2011 |
| Jaxal Limited | Professional & scientific | 2024 |
| JAY Halim Equine Limited | Agriculture & fishing | 2015 |
| JAY Roofing (Wiltshire) Ltd | Construction | 2018 |
| Jayvers Ltd | Real estate | 2018 |
| JB Concrete Coatings Specialist Ltd | Construction | 2025 |
| JB Precast Ltd | Construction | 2016 |
| JBT Accountancy Limited | Professional & scientific | 2019 |
| JC Combustion Services Limited | Construction | 2013 |
| Jcb-S Garden-Maintain Ltd | Administrative & support | 2021 |
| Jcia Properties Ltd | Real estate | 2025 |
| Jcwf Consulting Limited | Information & communication | 2025 |
| Jdhh Limited | Professional & scientific | 2020 |
| JDI Property Limited | Real estate | 2021 |