| Atmos Wave Ltd | Manufacturing | 2008 |
| Atmosphere Property Letting Ltd | Real estate | 2019 |
| ATN Global Limited | Other services | 2019 |
| ATN Productions Ltd | Information & communication | 2025 |
| Atns Solutions Limited | Hospitality | 2014 |
| Atoll Properties Limited | Real estate | 2004 |
| Atolye Ltd | Wholesale & retail | 2022 |
| Atom + Limited | Wholesale & retail | 2012 |
| Atom Marketing Ltd | Wholesale & retail | 2023 |
| Atomi Ltd | Manufacturing | 2018 |
| Atomic Creation Limited | Wholesale & retail | 2002 |
| Atop Gear Motors Ltd | Wholesale & retail | 2021 |
| Atoz Health Ltd | Wholesale & retail | 2021 |
| Atoz Serviced Apartments Ltd | Administrative & support | 2016 |
| Atoz Solutions Limited | Construction | 2025 |
| Atoz Traders Limited | Wholesale & retail | 2026 |
| Atozats Ltd | Information & communication | 2017 |
| ATP Accountancy Group Ltd | Financial services | 2023 |
| ATP Accountancy Ltd | Professional & scientific | 2022 |
| ATP Global Talent Ltd | Administrative & support | 2022 |
| ATP Instone Holdings Limited | Professional & scientific | 2008 |
| ATP Instone Limited | Professional & scientific | 2008 |
| ATP International Group Limited | Professional & scientific | 2006 |
| ATP UK Limited | Transport & logistics | 2007 |
| Atpi Limited | Professional & scientific | 2008 |
| Atpledge Limited | Financial services | 2012 |
| ATR Accountants Limited | Professional & scientific | 2016 |
| ATR Couriers Limited | Transport & logistics | 2025 |
| ATR Group Limited | Transport & logistics | 2023 |
| ATR Motors Ltd | Wholesale & retail | 2026 |
| ATR Real Estates Ltd | Real estate | 2023 |
| ATR Studio Ltd | Information & communication | 2026 |
| Atrax BNR Ltd | Professional & scientific | 2026 |
| Atreen Ltd | Health & social care | 2017 |
| Atregs Consulting Limited | Administrative & support | 2013 |
| Atreus Corporation Limited | Hospitality | 2025 |
| Atreus Global Limited | Professional & scientific | 2015 |
| Atrfood Limited | Hospitality | 2020 |
| Atrice Ltd | Professional & scientific | 2012 |
| Atrium City Living Limited | Real estate | 2003 |
| Atrium Coffee Roasters Limited | Manufacturing | 2025 |
| Atroxt for Supplies General Trading and Contracting Ltd | Wholesale & retail | 2026 |
| ATS (MCR) Ltd | Wholesale & retail | 2022 |
| ATS Accounting and Tax Solutions MCR Ltd | Professional & scientific | 2020 |
| ATS Auto Gadgets UK Limited | Wholesale & retail | 2020 |
| ATS Auto Sales & Repair Ltd | Wholesale & retail | 2024 |
| ATS Auto Services Ltd | Wholesale & retail | 2017 |
| ATS Building & Joinery Limited | Construction | 2026 |
| ATS Financial Services and Consultancy Limited | Financial services | 2025 |
| ATS Global Ltd | Wholesale & retail | 2025 |
| ATS Manchester North/Salford Ltd | Health & social care | 2021 |
| Atsg Apparel Limited | Wholesale & retail | 2023 |
| Atsp FIN Ltd | Wholesale & retail | 2025 |
| Atsu Information Technology Company Ltd | Other services | 2023 |
| ATT2 Ltd | Wholesale & retail | 2019 |
| Atta Residential Ltd | Real estate | 2025 |
| Attack Force Music Limited | Arts & recreation | 2018 |
| Attain Health & Safety Training (HST) Ltd | Education | 2023 |
| Attanta Limited | Financial services | 1995 |
| Attar Apparel 2 Limited | Wholesale & retail | 2021 |
| Attar Software Limited | Real estate | 2005 |
| Attarah Al-Yamamah Trading Ltd | Wholesale & retail | 2026 |
| Attarbashi Limited | Health & social care | 2019 |
| Attas Alamin Ltd | Education | 2025 |
| Attbi Properties Ltd | Real estate | 2022 |
| Attekus UK Ltd | Information & communication | 2025 |
| Attendeez Ltd | Education | 2023 |
| Attendist Ltd | Information & communication | 2021 |
| Attention Digital Marketing Ltd | Administrative & support | 2018 |
| Attentionit Limited | Information & communication | 2007 |
| Attentive Cleaners Ltd | Administrative & support | 2025 |
| Attentive Consulting Ltd | Other services | 2020 |
| Attg Ltd | Information & communication | 2022 |
| Attic Angel Ltd | Wholesale & retail | 2021 |
| Attic Home Ltd | Wholesale & retail | 2020 |
| Attic NE Limited | Construction | 2020 |
| Attica Sciences Ltd | Wholesale & retail | 2018 |
| Atticus Actuals Ltd | Health & social care | 2003 |
| Atticus IP Ltd | Wholesale & retail | 2019 |
| Atticus Legal (Nominees) Limited | Professional & scientific | 2008 |
| Atticus Promo Ltd | Wholesale & retail | 2019 |
| Attire Alliance Limited | Wholesale & retail | 2025 |
| Attire Apparels Limited | Wholesale & retail | 2015 |
| Attivo Care Limited | Health & social care | 2019 |
| Attivo Properties Limited | Real estate | 2023 |
| Attock Worldwide Traders Ltd | Wholesale & retail | 2026 |
| Attoh Ltd | Information & communication | 2022 |
| Attraction Associates Ltd | Professional & scientific | 2020 |
| Attraction Clothing Co. Limited | | 1986 |
| Attraction Cosmetics Ltd | Wholesale & retail | 2024 |
| Attractor Mobile Ltd | Information & communication | 2015 |
| Attwells Limited | Wholesale & retail | 2025 |
| Attwood Associates Ltd | Administrative & support | 2009 |
| Attwood Drake Ltd | Construction | 2014 |
| Atuah Osteopathy Limited | Health & social care | 2025 |
| Atuns Ltd | Information & communication | 2010 |
| Atura Group Limited | Wholesale & retail | 2025 |
| Atvenu UK Ltd | Information & communication | 2025 |
| ATW Prestige Co Ltd | Wholesale & retail | 2025 |
| Atwa Distribution Ltd | Wholesale & retail | 2024 |