| Irwin & Wilcox Support Services Limited | Information & communication | 2011 |
| Isabel Browning Limited | Information & communication | 2021 |
| Isabelle Essome Group Ltd | Wholesale & retail | 2022 |
| Isambard Property Ltd | Real estate | 2024 |
| Isborne Ltd | Financial services | 2021 |
| Isbourne Environmental Limited | Professional & scientific | 1991 |
| Isbourne Publishing Ltd | Information & communication | 2023 |
| Isbourne Valley Limited | Real estate | 2025 |
| ISG Renewables Limited | Energy | 2022 |
| Isie Developments Limited | Construction | 2019 |
| Islcollections Limited | Administrative & support | 2017 |
| Isledene Limited | Households | 1977 |
| Ismart Phone Care Ltd | Wholesale & retail | 2025 |
| ISO 3D Limited | Professional & scientific | 2014 |
| Isobel Davidson Communications Limited | Professional & scientific | 2019 |
| ISW Systems Limited | Manufacturing | 2015 |
| IT Services Livonia Limited | Information & communication | 2011 |
| IT Support Berkshire Limited | Information & communication | 2011 |
| Ital Scooters Ltd | Wholesale & retail | 2009 |
| Itecnic Limited | Manufacturing | 2015 |
| Itectric Ltd | Construction | 2006 |
| ITEM2 Ltd | Manufacturing | 2004 |
| Iteration LAB Ltd | Information & communication | 2026 |
| Itman Tech Ltd | Wholesale & retail | 2013 |
| ITR Advisors Limited | Professional & scientific | 2019 |
| Itransfer Ltd | Transport & logistics | 2024 |
| ITS Academy Limited | Education | 2014 |
| ITS for YOU Ltd | Real estate | 2003 |
| ITS Recruiting Limited | Administrative & support | 2022 |
| Itsa Education Limited | Information & communication | 2008 |
| Itwi Ltd | Information & communication | 2025 |
| IV Cleaning 2023 Limited | Administrative & support | 2023 |
| Ives & Co Financial Services Limited | Financial services | 2003 |
| IVO AI UK, Ltd | Administrative & support | 2026 |
| Ivory Doors Limited | Manufacturing | 2023 |
| IVY Contracting (Midlands) Limited | Construction | 2007 |
| IVY2 Limited | Financial services | 2025 |
| Iwob Consulting Ltd | Professional & scientific | 2025 |
| Izabela Holiday LET Ltd | Hospitality | 2026 |
| Izabela Rachwal Ltd | Real estate | 2024 |
| IZI Logistics Ltd | Transport & logistics | 2024 |
| Izzy Specialist Finance Ltd | Financial services | 2023 |
| J & C Properties Cheltenham Ltd | Real estate | 2022 |
| J & E Agri Limited | Agriculture & fishing | 2020 |
| J & I Limited | Professional & scientific | 2009 |
| J & M Property Development Limited | Real estate | 2020 |
| J & O Flowers Ltd | Wholesale & retail | 2021 |
| J & S Engineering (UK) Ltd | Manufacturing | 2003 |
| J & T Racing Ltd | Arts & recreation | 2025 |
| J & W Leisure Ltd | Administrative & support | 2023 |
| J and H.L. Harkness LLP | | 2004 |
| J and J Care Services Ltd | Health & social care | 2009 |
| J APS Stores (Holding) Ltd | Financial services | 2019 |
| J B M Access Services Limited | Construction | 2013 |
| J B Plastering & Drylining Ltd | Construction | 2017 |
| J Baker Electrical Ltd | Construction | 2023 |
| J Barter Holiday Lets Ltd | Real estate | 2024 |
| J Barter Properties Limited | Real estate | 2023 |
| J Birch Consultancy Ltd | Other services | 2024 |
| J Carter Consultancy Limited | Professional & scientific | 2019 |
| J Chess Property Consultants Ltd | Professional & scientific | 2020 |
| J Churchill Construction Limited | Construction | 2003 |
| J D Metal Supplies Limited | Wholesale & retail | 2012 |
| J D Zencare Limited | Health & social care | 2013 |
| J F Building Services (UK) Ltd | Extraterritorial | 2008 |
| J F Smit Limited | Health & social care | 2013 |
| J G G Group Ltd | Wholesale & retail | 2018 |
| J Gilder Earthmoving & Aggregates Ltd | Water & waste | 2018 |
| J Howley Brickwork Ltd | Administrative & support | 2017 |
| J Lakin Ltd | Professional & scientific | 2025 |
| J Lewis & Sons Limited | Construction | 2024 |
| J M Clegg Ltd | Professional & scientific | 2020 |
| J M Gibson & M V Kyle Ltd | Health & social care | 2010 |
| J M Hayden Limited | Construction | 2011 |
| J M Sullivan Limited | Other services | 2020 |
| J M Weston (Construction) Limited | Construction | 2004 |
| J M Weston (Construction) Trustees Limited | Other services | 2025 |
| J Nicholls & Associates Ltd | Professional & scientific | 2010 |
| J O Care Services Ltd | Financial services | 2020 |
| J O'Neill IT Services Ltd | Information & communication | 2017 |
| J P Premier Fitness Ltd | Other services | 2019 |
| J Perrett Plumbing & Heating Ltd | Construction | 2012 |
| J Pugh Consultancy Limited | Professional & scientific | 2023 |
| J Reid Property Investments Limited | Real estate | 2020 |
| J S Carpets Holdings Limited | Extraterritorial | 2002 |
| J S Carpets Limited | Wholesale & retail | 2002 |
| J S LEE Civils Ltd | Construction | 2020 |
| J Spencer Consulting Ltd | Information & communication | 2022 |
| J Stephens Consultancy Ltd | Professional & scientific | 2015 |
| J T Spencer Associates Ltd | Professional & scientific | 2014 |
| J White Carpentry Ltd | Manufacturing | 2019 |
| J White Joinery Ltd | Construction | 2019 |
| J Whitehead Farriers & Co Ltd | Agriculture & fishing | 2015 |
| J Worthy Consultancy Ltd | Information & communication | 2019 |
| J Z (BD) Property Limited | Real estate | 2025 |
| J&M Developments (Gloucestershire) Ltd | Construction | 2022 |
| J. Cawthorne Ltd | Information & communication | 2008 |
| J. Hennessy Ltd | Hospitality | 2011 |
| J.A. Gadd Limited | Manufacturing | 1974 |
| J.Clarke Properties Ltd | Real estate | 2020 |