| Adviser Rankings Limited | Information & communication | 2012 |
| AE Property Services Ltd | Construction | 2021 |
| Aeca Consulting Limited | Professional & scientific | 2015 |
| Aeca Imagination Limited | Education | 2017 |
| AED360 Ltd | Wholesale & retail | 2019 |
| Aerial TEC (London & SE) Ltd | Administrative & support | 2006 |
| Aerismed Consulting Limited | Transport & logistics | 2023 |
| Aerolis Technologies Limited | Professional & scientific | 2025 |
| Aerospace Maintenance Advisors Ltd | Manufacturing | 2026 |
| Aetherleaf Ltd | Information & communication | 2026 |
| Aetherline Limited | Professional & scientific | 2025 |
| Aetos Services Limited | Construction | 2026 |
| AFF E-Commerce Ltd | Wholesale & retail | 2025 |
| Affinity Insurance Solutions Limited | Financial services | 2020 |
| Affordable Accounting Services Limited | Professional & scientific | 2018 |
| AFG Mentoring Ltd | Education | 2026 |
| Afis Consultancy Limited | Information & communication | 2017 |
| Afmk Limited | Professional & scientific | 2019 |
| African Style BBQ Wood Ltd | Wholesale & retail | 2025 |
| AFS Psychiatric Consultancy Services Limited | Health & social care | 2017 |
| AG International Recruitment Limited | Education | 2026 |
| AG Projects Groundworks Ltd | Construction | 2025 |
| AG Vision Ltd | Professional & scientific | 2020 |
| Agaci Ltd | Real estate | 2026 |
| Agamemnon Real Estate Ltd | Real estate | 2018 |
| Agile Services Ltd | Information & communication | 2007 |
| Agios Capital Ltd | Administrative & support | 2014 |
| Aglaze Aviation Limited | Manufacturing | 2018 |
| Aglaze International Limited | Manufacturing | 2016 |
| Agnes Wade & Co Ltd | Wholesale & retail | 2023 |
| Agriloomis Ltd | Wholesale & retail | 2026 |
| AGS Investments (2023) Ltd | Financial services | 2023 |
| AGS Property Investments (2015) Limited | Real estate | 2015 |
| AH Associates Ltd | Administrative & support | 2008 |
| AH Lockett Ltd | Professional & scientific | 2024 |
| AH Partnership Limited | Professional & scientific | 2004 |
| Ahld Holdings Limited | Real estate | 2024 |
| AHP Architects and Surveyors Limited | Professional & scientific | 2002 |
| AI Morrison Ltd | Real estate | 2023 |
| Aidan Potter Design Studio Ltd | Professional & scientific | 2023 |
| Aidstar Limited | Information & communication | 2024 |
| AIM Sustain Ltd | Professional & scientific | 2022 |
| Aimes Advisory Ltd | Extraterritorial | 2024 |
| Aione Consulting Limited | Information & communication | 2025 |
| Air Cool Environmental Ltd | Construction | 2002 |
| Air Pathology Ltd | Professional & scientific | 2017 |
| Air Pressure Solutions Ltd | Manufacturing | 2013 |
| Airgen Limited | Energy | 1999 |
| Airspace Software Limited | Information & communication | 1999 |
| Airstruct Ltd | Construction | 2026 |
| Aiston Group Ltd | Information & communication | 2024 |
| AIT Colorsolve Limited | Other services | 2012 |
| Ajig Properties Ltd | Real estate | 2021 |
| AJK Holdings Ltd | Construction | 2015 |
| AJM 2020 Limited | Transport & logistics | 2020 |
| AK Acoustics Ltd | Professional & scientific | 2017 |
| AK2024 Property Ltd | Real estate | 2024 |
| Akita Property Development Limited | Construction | 2019 |
| Akrostix Limited | Arts & recreation | 2026 |
| Al&Aa Holdings Limited | Professional & scientific | 2025 |
| Alacrity Consulting Ltd | Professional & scientific | 2021 |
| Alan Johnson Vehicle Repairs Limited | Manufacturing | 2002 |
| Alan Wheatley Investments Limited | Professional & scientific | 2015 |
| ALB Steel Ltd | Construction | 2019 |
| Alb-Polska Ltd | Real estate | 2020 |
| Albatross Marine Claims Ltd | Professional & scientific | 2022 |
| Alcatoser Ltd | Administrative & support | 2026 |
| Alcides LLP | | 2001 |
| Alderwey Limited | Extraterritorial | 2008 |
| Alford & Bishop Legal Recruitment Limited | Professional & scientific | 2000 |
| Alfred & Austin Associates Limited | Professional & scientific | 2012 |
| Alfred & William Limited | Professional & scientific | 2019 |
| Alfred Austin Holdings Ltd | Financial services | 2014 |
| Alfred Austin Recruitment Ltd | Administrative & support | 2014 |
| Alfred Lloyd Ltd | Hospitality | 2017 |
| Algerie Motors Ltd | Professional & scientific | 2019 |
| Algomind Limited | Information & communication | 2016 |
| Algotec Ltd | Information & communication | 2019 |
| Alice Murray Healthcare Partners Ltd | Health & social care | 2026 |
| Alice Wang & Co. Ltd | Wholesale & retail | 2025 |
| Alidac UK Limited | Wholesale & retail | 2025 |
| Alien Interaction Media Limited | Administrative & support | 2026 |
| Alkemin Consulting Limited | Professional & scientific | 2026 |
| ALL About the Landscape Ltd | Manufacturing | 2025 |
| ALL Access Pass Music Limited | Information & communication | 2024 |
| ALL City Scaffolding Ltd | Construction | 2014 |
| ALL Door Solutions Limited | Construction | 2026 |
| ALL Equestrian Ltd | Agriculture & fishing | 2011 |
| ALL in One Bathrooms Ltd | Construction | 2021 |
| ALL in One Chimneys LLP | | 2026 |
| ALL in One Garden & Landscaping LLP | | 2025 |
| ALL in One Home Building LLP | | 2025 |
| ALL in One Home Decorating LLP | | 2025 |
| ALL in One Home Kitchens LLP | | 2025 |
| ALL in One Home Maintenance Ltd | Construction | 2021 |
| ALL in One Home Projects LLP | | 2025 |
| ALL in One Home Refurbishments Ltd | Construction | 2021 |
| ALL in One Home Services Ltd | Construction | 2014 |
| ALL in One Painting & Decorating Limited | Construction | 2014 |
| ALL in One Projects Ltd | Construction | 2021 |