| 9TH Floor Properties Ltd | Real estate | 2025 |
| A & a Residential Ltd | Real estate | 2022 |
| A & M Heating (UK) Limited | Construction | 2007 |
| A & T Building Services Limited | Construction | 2020 |
| A B Film and TV Limited | Transport & logistics | 2014 |
| A Cunningham Holdings Limited | Financial services | 2023 |
| A F H Consultancy Limited | Professional & scientific | 2013 |
| A F O'Connor Consulting Limited | Professional & scientific | 2017 |
| A Fold of Chairs Ltd | Wholesale & retail | 2023 |
| A G H Metals Limited | Construction | 2025 |
| A Just in Time Services Ltd | Other services | 2016 |
| A Karak Affair Ltd | Hospitality | 2025 |
| A King Medical Ltd | Health & social care | 2014 |
| A Latter & Company Limited | Wholesale & retail | 1935 |
| A Level-Up Limited | Construction | 2022 |
| A M Tooling Ltd | Wholesale & retail | 2019 |
| A N Tiling Limited | Construction | 2019 |
| A R F a Consulting Ltd | Professional & scientific | 2009 |
| A Solutions International Limited | Wholesale & retail | 2026 |
| A Sutton Limited | Professional & scientific | 2009 |
| A to Z Gardening Landscaping Services Ltd | Administrative & support | 2015 |
| A&B Electrics (Herts) Ltd | Construction | 2017 |
| A&D Innovations Limited | Administrative & support | 2025 |
| A&S Feet Ltd | Health & social care | 2022 |
| A&Sh Construction Ltd | Construction | 2024 |
| A&T Marketing Group Ltd | Information & communication | 2021 |
| A-Tay Property Ltd | Real estate | 2025 |
| A-Z Property Specialist Ltd | Construction | 2018 |
| A.D Plumbing & Drainage Ltd | Construction | 2022 |
| A.N.E Consult Ltd | Professional & scientific | 2013 |
| A.Ward Cleaning Limited | Administrative & support | 2026 |
| A1 Motortech Limited | Wholesale & retail | 2026 |
| A1 Pestmasters Limited | Administrative & support | 2010 |
| A1 Taxis Wolverhampton Ltd | Other services | 2023 |
| A2B Express Limited | Transport & logistics | 2018 |
| AA Facades Limited | Construction | 2015 |
| AA Realisations Limited | Information & communication | 2014 |
| AAA Quote Solution UK Ltd | Hospitality | 2020 |
| Aaban Cuisine Ltd | Administrative & support | 2017 |
| Aace Fitness Consultants Limited | Arts & recreation | 2020 |
| Aaditya Trading Limited | Wholesale & retail | 2025 |
| AAF Contractors Ltd | Construction | 2022 |
| Aardvark Bathrooms Limited | Wholesale & retail | 2024 |
| Aarkd Properties Ltd | Real estate | 2023 |
| Aaron Meredith Tennis Ltd | Arts & recreation | 2026 |
| Aath Financial Services Ltd | Information & communication | 2017 |
| Aawk Limited | Real estate | 2024 |
| Abacaxi Consulting Limited | Professional & scientific | 2019 |
| ABAMR2 Ltd | Financial services | 2016 |
| Abbey Bowmen (Herts) Limited | Arts & recreation | 2025 |
| Abbey Gateway Enterprises Limited | Administrative & support | 1997 |
| Abbey Law Limited | Professional & scientific | 2019 |
| Abbey Lodge Care Home Ltd | Health & social care | 2014 |
| Abbey Plumbing & Heating (St.Albans) Limited | Construction | 2023 |
| Abbey Theatre Trust (ST. Albans) Limited(The) | Arts & recreation | 1966 |
| Abbi Ltd | Professional & scientific | 2015 |
| Abbots Care Limited | Administrative & support | 2001 |
| Abbots Care Property Limited | Real estate | 2022 |
| Abbots Care Training Limited | Other services | 2007 |
| Abbots Friends Limited | Health & social care | 2019 |
| Abbots Specialist Care Limited | Administrative & support | 2017 |
| Abbotswood DCL Ltd | Real estate | 2016 |
| ABC Advisory Services Limited | Financial services | 2015 |
| ABC Fencing Limited | Construction | 2012 |
| Abc-Xyz Childcare Ltd | Health & social care | 2016 |
| Abcl Accounting Ltd | Professional & scientific | 2022 |
| Aberley Limited | Professional & scientific | 1996 |
| Abfly Distribution Ltd | Administrative & support | 2026 |
| ABK Building Supplies Ltd | Wholesale & retail | 2016 |
| About Time ST Albans Ltd | Wholesale & retail | 2025 |
| Above Construction Limited | Professional & scientific | 2018 |
| Absolut Services Limited | Other services | 2005 |
| Absolute Assets Consulting Ltd | Administrative & support | 2023 |
| Absolute Market Research Limited | Professional & scientific | 2014 |
| ABT Logic Limited | Professional & scientific | 2024 |
| Abutchart Business Services Ltd | Information & communication | 2023 |
| ABW Group Ltd | Information & communication | 2017 |
| Abyss Global Ltd | Professional & scientific | 2012 |
| AC and S Investments Ltd | Real estate | 2016 |
| AC Engineering and Technical Translations Limited | Professional & scientific | 2023 |
| AC Plumbing and Heating Ltd | Construction | 2026 |
| AC2000 Holdings Ltd | Financial services | 2026 |
| ACA Hair Limited | Other services | 2004 |
| Acacias IT Solutions Limited | Information & communication | 2013 |
| Academy Residences Limited | Education | 2013 |
| Acao Social Ltd | Arts & recreation | 2022 |
| Accipio Digital Ltd | Professional & scientific | 2017 |
| Accipio Leadership Ltd | Professional & scientific | 2017 |
| Accipio Limited | Information & communication | 2010 |
| Accopharm Clinical Trial Services Limited | Professional & scientific | 2019 |
| Accord HR Consulting Ltd | Professional & scientific | 2019 |
| Accountability Partners Limited | Professional & scientific | 2024 |
| Accountancy Search Ltd | Administrative & support | 2024 |
| Accountinext Ltd | Professional & scientific | 2019 |
| Accounting for YOU Limited | Professional & scientific | 2008 |
| Accounting Solutions (Herts) Limited | Administrative & support | 2016 |
| Accura-Search Ltd | Professional & scientific | 2025 |
| Ace Claims and Bodyworks Ltd | Wholesale & retail | 2024 |
| Ace Construction Group Ltd | Construction | 2024 |
| Ace Fencing (Southern) Limited | Construction | 2013 |