| A M GAS Solutions Limited | Professional & scientific | 2017 |
| A M Property Investments (2019) Limited | Real estate | 2019 |
| A P Circle Ltd | Real estate | 2020 |
| A Plus Aluminium Limited | Extraterritorial | 2007 |
| A Plus Windows & Doors Limited | Manufacturing | 1986 |
| A Rattansi Ltd | Education | 2025 |
| A Reed Contracting Ltd | Professional & scientific | 2013 |
| A Shan and Sons Ltd | Real estate | 2025 |
| A Slice of Happiness Innate Health Community Interest Company | Health & social care | 2024 |
| A Spiritual Occasion Limited | Other services | 2020 |
| A Squared Properties Ltd | Real estate | 2020 |
| A Star Assured Property Management Limited | Real estate | 2013 |
| A Star Nails 2 Limited | Other services | 2020 |
| A Stars Driving School Ltd | Education | 2019 |
| A to Z Group Limited | Real estate | 2016 |
| A Tunnel Wood Limited | Professional & scientific | 2024 |
| A Twenty Four Ltd | Wholesale & retail | 2026 |
| A Violet Tech Ltd | Information & communication | 2025 |
| A Y Ashbel Limited | Real estate | 2018 |
| A&A Signature Developments Ltd | Construction | 2025 |
| A&C Skills Ltd | Construction | 2018 |
| A&C Smart Services Ltd | Manufacturing | 2024 |
| A&D Brickwork Ltd | Construction | 2015 |
| A&D Building Services Ltd | Construction | 2018 |
| A&Dicare Ltd | Health & social care | 2025 |
| A&E Expert Consulting Ltd | Professional & scientific | 2023 |
| A&E Expert Properties Ltd | Real estate | 2024 |
| A&G and SON Ltd | Construction | 2025 |
| A&G Transfer Ltd | Transport & logistics | 2024 |
| A&H Buildcore Construction Ltd | Construction | 2026 |
| A&H Construction Consultants Ltd | Construction | 2026 |
| A&H Homes Limited | Real estate | 2017 |
| A&J Polonia Residence Apartment Ltd | Real estate | 2025 |
| A&K Universe Ltd | Wholesale & retail | 2025 |
| A&L Extensions Ltd | Construction | 2019 |
| A&M Psych Ltd | Health & social care | 2022 |
| A&R Heating and Plumbing Services Ltd | Construction | 2022 |
| A&S Glory Limited | Wholesale & retail | 2021 |
| A&S Property Concepts Limited | Construction | 2020 |
| A&S UK Private Ltd | Wholesale & retail | 2023 |
| A&S Wellness and Success Ltd | Arts & recreation | 2022 |
| A&T Pro Clean Services Ltd | Construction | 2024 |
| A&T Residential Ltd | Real estate | 2026 |
| A&W Software UK Limited | Administrative & support | 2012 |
| A-Clinic Ltd | Other services | 2022 |
| A-Dem Demolition Ltd | Construction | 2021 |
| A-H Rose Ltd | Wholesale & retail | 2020 |
| A-Kind Limited | Health & social care | 2015 |
| A-Star Watches Ltd | Wholesale & retail | 2023 |
| A. J. B. Denture Services Ltd | Health & social care | 2005 |
| A.A. Effects Ltd | Information & communication | 2016 |
| A.A. Fisher (Holdings) Limited | Professional & scientific | 2005 |
| A.A. Fisher (Investments) Limited | Real estate | 2015 |
| A.A. Fisher (Property Services) Limited | Administrative & support | 2015 |
| A.A. Fisher (Trading) Limited | Administrative & support | 2005 |
| A.B.M.Chemicals Limited | Professional & scientific | 1931 |
| A.F.K. Contracts Limited | Wholesale & retail | 1999 |
| A.G.E. (Worldwide) Limited | Wholesale & retail | 2011 |
| A.H Removal and Storage Limited | Transport & logistics | 2024 |
| A.Ilendo Property Development Two Ltd | Real estate | 2026 |
| A.Maclean Transport Services Ltd | Transport & logistics | 2023 |
| A.O.Imaging Ltd | Health & social care | 2023 |
| A.R.Beveridge & Sons Ltd | Construction | 2018 |
| A.S. Profinterlux Ltd | Construction | 2017 |
| A.S.C. Invest LLP | | 2004 |
| A.T.N.A Investments Ltd | Real estate | 2023 |
| A1 Cabs Watford Ltd | Transport & logistics | 2026 |
| A1 Car Shop Ltd | Wholesale & retail | 2024 |
| A1 Executive Travel Group Ltd | Administrative & support | 2016 |
| A1 Home Developments Ltd | Construction | 2024 |
| A1 Laundrette Ltd | Other services | 2023 |
| A1 PAY Limited | Construction | 2024 |
| A1 Property Finance Ltd | Financial services | 2024 |
| A10 Parts and Service Limited | Wholesale & retail | 2021 |
| A13EAVS Limited | Construction | 2024 |
| A1BA Ltd | Manufacturing | 2018 |
| A1PERFUME Ltd | Wholesale & retail | 2025 |
| A2 Brickwork Ltd | Construction | 2018 |
| A2 Events Ltd | Hospitality | 2026 |
| A2 Natures Ltd | Wholesale & retail | 2026 |
| A2A Heat Pumps Limited | Professional & scientific | 2020 |
| A2B Taxi and Private Hire Watford Ltd | Transport & logistics | 2025 |
| A2K Holdings Limited | Financial services | 2022 |
| A2K Midco Limited | Financial services | 2019 |
| A2K Topco Limited | Financial services | 2019 |
| A2Y Solutions Ltd | Manufacturing | 2025 |
| A2Z Home Care Services Limited | Public administration | 2020 |
| A3 Capital Partners Ltd | Professional & scientific | 2026 |
| A3 Immaculate Global Ltd | Wholesale & retail | 2025 |
| AA Cash Express Ltd | Administrative & support | 2024 |
| AA Fintech Limited | Information & communication | 2017 |
| AA Platinum Ltd | Administrative & support | 2018 |
| AA Trains Ltd | Arts & recreation | 2025 |
| AAA Cars (UK) Ltd | Transport & logistics | 2013 |
| AAA Cricket Ltd | Arts & recreation | 2024 |
| AAA Distribution Ltd | Transport & logistics | 2026 |
| AAA Enterprise Ltd | Real estate | 2024 |
| AAA Interiors Ltd | Construction | 2024 |
| AAA Legal Ltd | Professional & scientific | 2018 |
| Aaaa Decor and Services Ltd | Construction | 2024 |