| JMP Civil Engineering Ltd | Professional & scientific | 2016 |
| JNA Dental Limited | Health & social care | 2025 |
| JNT Care Solutions Limited | Professional & scientific | 2009 |
| JO Marshall Fraser Ltd | Wholesale & retail | 2018 |
| JO Nixon Limited | Administrative & support | 2019 |
| JO Renshaw Life Coach Ltd | Professional & scientific | 2020 |
| JO Wright Limited | Education | 2000 |
| JOB Plumbing & Repairs Ltd | Construction | 2025 |
| Jobsocks Ltd | Other services | 2018 |
| Jody Shaw Designs Limited | Professional & scientific | 2026 |
| Jody Thomas Driver Training Ltd | Education | 2022 |
| JOE Perkins Design Ltd | Professional & scientific | 2012 |
| Joeies Convenience Store Ltd | Wholesale & retail | 2019 |
| Jogd Limited | Information & communication | 2026 |
| John Halbert Consulting Ltd | Information & communication | 2013 |
| John Mitchell Management Consultancy Ltd | Professional & scientific | 2016 |
| John Rodway Limited | Other services | 2019 |
| Johnston Homes Ltd | Real estate | 2015 |
| Johnston Investments Ltd | Real estate | 2013 |
| Jointing ID Ltd | Construction | 2020 |
| Jolly Pirate Ltd | Wholesale & retail | 2022 |
| JON Slinger Productions Ltd | Arts & recreation | 2015 |
| Jones & Jones Dental Limited | Health & social care | 2023 |
| Jones Bros.(B'Ton)Limited | Real estate | 1960 |
| Jones Brothers Property Ltd | Real estate | 2025 |
| Jones Electrical Contracting Ltd | Construction | 2024 |
| Jones Thought Leadership Ltd | Professional & scientific | 2025 |
| Jose Costa Limited | Health & social care | 2015 |
| Joseph Baldwin & Lawrenson Ltd | Administrative & support | 2019 |
| Joseph GAS Services Limited | Construction | 2008 |
| Joseph Peissel Consulting Ltd | Professional & scientific | 2022 |
| Josta Developments Ltd | Real estate | 2025 |
| Journey to Reconnect Limited | Health & social care | 2026 |
| Joy City Limited | Real estate | 2024 |
| Joy Concerts Ltd | Arts & recreation | 2017 |
| Joy Media Services Ltd | Professional & scientific | 2020 |
| Joyce & Karl Limited | Financial services | 2020 |
| Joyn Bags Ltd | Wholesale & retail | 2022 |
| JP Dental Limited | Health & social care | 2023 |
| JP Photographic Limited | Professional & scientific | 2003 |
| Jppp Properties Limited | Real estate | 2021 |
| JPT Translation Ltd | Professional & scientific | 2018 |
| JPZ Cleaning Ltd | Administrative & support | 2016 |
| JR PVT Ltd | Hospitality | 2020 |
| JRB Holidays Limited | Hospitality | 2009 |
| JRS Services Limited | Administrative & support | 2019 |
| Jrsr Property Limited | Real estate | 2023 |
| JSR Consultants Limited | Professional & scientific | 2025 |
| JST Lynwood Ltd | Health & social care | 2025 |
| Jsupplies Limited | Wholesale & retail | 2023 |
| JT Brighton Limited | Wholesale & retail | 2024 |
| JT Medical Group Limited | Health & social care | 2017 |
| JT Propery Development Limited | Real estate | 2026 |
| JTR Property Ltd | Real estate | 2023 |
| Judd Management Services Limited | Administrative & support | 2012 |
| Juicybowls Limited | Extraterritorial | 2023 |
| Julie Binchet Designs Ltd | Arts & recreation | 2009 |
| Juliet Cooper Admin Services Limited | Administrative & support | 2016 |
| Juliet Fawcett Medical Writing Ltd | Other services | 2017 |
| Juliet Mayhew Limited | Wholesale & retail | 2019 |
| Jumbobright Limited | Real estate | 1988 |
| Jump Media Ltd | Professional & scientific | 2025 |
| Jump Recruit Ltd | Administrative & support | 2023 |
| Jumpinwestsussex Ltd | Arts & recreation | 2019 |
| Jungle Butter Ltd | Wholesale & retail | 2020 |
| Jungle Light Ltd | Information & communication | 2005 |
| Jungle Penguin Limited | Information & communication | 2015 |
| Juno Pictures Ltd | Education | 2023 |
| Jupiter Express Ltd | Wholesale & retail | 2018 |
| Just About Community Ltd | Information & communication | 2022 |
| Just Construction (Southern) Limited | Construction | 2000 |
| Just Like Home Childcare Limited | Health & social care | 2019 |
| Just SO Clothing & Merchandise Limited | Administrative & support | 2009 |
| Justbean Software Limited | Information & communication | 2000 |
| Justice Legal Ltd | Professional & scientific | 2025 |
| Justin Hyde Ltd | Professional & scientific | 2025 |
| Justin Residents Association Limited | Households | 1976 |
| JVH Holdings Ltd | Financial services | 2025 |
| JW Scaffolding UK Limited | Construction | 2024 |
| JWB Group Ltd | Construction | 2016 |
| JWL Sussex Ltd | Construction | 2024 |
| JWP Holdings Ltd | Real estate | 2024 |
| JZT Consulting Ltd | Information & communication | 2019 |
| Jötnar Limited | Construction | 2025 |
| K C Metal Works Limited | Manufacturing | 2017 |
| K Dental Aesthetics Limited | Health & social care | 2026 |
| K of GSM Brighton Limited | Transport & logistics | 2009 |
| K&A Venture Group Ltd | Real estate | 2021 |
| K&A Venture Properties Ltd | Real estate | 2022 |
| K&P Motor Services Limited | Wholesale & retail | 2020 |
| K-Nails Studio Ltd | Other services | 2021 |
| K. P. Spaces Ltd | Real estate | 2019 |
| K.A.L Homes Ltd | Construction | 2011 |
| K2 Collective Limited | Wholesale & retail | 2024 |
| K3B Ltd | Construction | 2019 |
| K6 Ltd | Other services | 2022 |
| Kachope Enterprises Ltd | Health & social care | 2025 |
| Kadous Ltd | Wholesale & retail | 2016 |
| Kaduna Properties Limited | Real estate | 2009 |
| Kahy Limited | Arts & recreation | 2010 |