| ATA Physiotherapy Ltd | London | 2022 |
| ATA Translations Limited | Hampshire | 1983 |
| Atacanter Limited | St Ives | 2014 |
| Ataksak International Limited | Cambridge | 2022 |
| Atalanta Marine Ltd | London | 2026 |
| Atalanta Motors Limited | Stone | 2009 |
| Atalta Ltd | Reading | 2015 |
| Atama Healt & Wellness Ltd | London | 2018 |
| Atanas Ivanov Zlatkov Ltd | Farnborough | 2024 |
| Atanasius Limited | Canterbury | 2013 |
| Atanda Group Ltd | Uxbridge | 2015 |
| Atcf Member Ltd | London | 2021 |
| ATD Aerospace Engineering Ltd | St Helens | 2014 |
| ATD Brand Limited | Oswestry | 2025 |
| ATD Eras Limited | Manchester | 2021 |
| ATD Photography Ltd | Telford | 2010 |
| ATD Property Maintenance Limited | Maidenhead | 2009 |
| ATE Electrical Ltd | Alfreton | 2024 |
| ATE Testing Service Ltd. | Cambridge | 2016 |
| ATE Truck & Trailer Sales Limited | London | 1994 |
| Ateco Technology Ltd | West Midlands, England, | 2015 |
| Atek Turkey Ltd | London | 2025 |
| Atelier Design Studio Limited | Salford | 2014 |
| Atelier Designs (UK) Limited | Stourbridge | 1994 |
| Atelier Jewellery Limited | Blackburn | 2023 |
| Atelier Texture Ltd | London | 2023 |
| Atenso Limited | High Wycombe | 2019 |
| Atex Worldwide Ltd | Southampton | 2020 |
| ATG Airports (Products) Limited | Warrington | 2007 |
| ATG Broadcast Limited | Reading | 2014 |
| ATG Foods Ltd | Dagenham | 2025 |
| ATG Oxford Limited | Oxford | 1998 |
| ATG RTM Company Limited | Bournemouth | 2005 |
| ATG Spectrum (UK) Limited | Reading | 2001 |
| ATG Travel Services Ltd | York | 2025 |
| ATH Online Learning Ltd | Leeds | 2014 |
| Athari Infrastructure Development Ltd | Northampton | 2017 |
| Athawes Estates UK Limited | Hungerford | 2025 |
| Athena & Eden Ltd | London | 2023 |
| Athena 1973 Limited | Alton | 2013 |
| Athena Accounting and Bookkeeping Services Ltd | London | 2022 |
| Athena Aerospace Ltd | Preston | 2025 |
| Athena Care Homes Limited | Laindon | 2014 |
| Athena Control Limited | Maidstone | 2022 |
| Athena Creations Limited | Cramlington | 2020 |
| Athena DRY Cleaners Ltd | London | 1999 |
| Athena Educational Consult Ltd | Mansfield | 2022 |
| Athena Marketing (UK) Limited | Hartford | 1992 |
| Athene Coaching Limited | Macclesfield | 2023 |
| Atheneum Global Ltd | London | 2020 |
| Athenian Property Developments Ltd | Southampton | 2020 |
| Athergift Limited | Stoke-On-Trent | 1998 |
| Atherstone Mobile Valeting Ltd | London | 2019 |
| Atherton and Cookson Limited | Preston | 2021 |
| Atherton Hall Residents Association Limited | Atherton | 1991 |
| Athipo Limited | London | 2010 |
| Athlon Limited | London | 2012 |
| Athlone Homes Limited | Watford | 2010 |
| Athos Sounds Ltd | | 2006 |
| ATI SIP Trustees 1 Limited | Woking | 2015 |
| ATI SIP Trustees 2 Limited | Woking | 2015 |
| Atib Services (UK) Limited | London | 2001 |
| Atic Banbury Limited | Buckingham | 2015 |
| Aticfour Limited | Buckingham | 2022 |
| Atik Yachting Ltd | London | 2024 |
| Atil Sail Limited | London | 2025 |
| Atina Films Ltd | Bedford | 2012 |
| Atisa Ltd | London | 2025 |
| Atithi Indian Cuisine Ltd | Hampton | 2010 |
| ATK Gardens Limited | Bristol | 2018 |
| Atkin & SON Limited | Mansfield | 2017 |
| Atkin Automation Limited | Wakefield | 2014 |
| Atkin BHP Limited | Wakefield | 2014 |
| Atkins Bros. (Syston) Limited | Syston | 1980 |
| Atkins Consulting Ltd | Verwood | 2011 |
| Atkins of Hinckley Limited | Sutton-In-Ashfield | 1929 |
| Atkins Pension Trustee Limited | Epsom | 2009 |
| Atkins PMC Limited | Great Dunmow | 2012 |
| Atkinson & James Limited | Northwich | 2016 |
| Atkinson Builders (Leeds) Ltd | Leeds | 2012 |
| Atkinson Forecourt Group Limited | Carlisle | 2019 |
| Atkinson House Management Company Limited | Weston-Super-Mare | 2007 |
| Atkinson Properties Limited | Blackburn | 2000 |
| Atkinson X Valmont Limited | London | 2026 |
| Atkinsons Bullion & Coins Limited | London | 2015 |
| Atkinsons Bullion Limited | London | 2013 |
| Atkinsons Coins & Bullion Limited | London | 2013 |
| Atkinsons Coins Limited | London | 2013 |
| Atkinsons the Jewellers Limited | London | 2013 |
| Atkinsréalis Kins Holdings Limited | Surrey | 1961 |
| ATL Europe (France) Limited | Ferndown | 2019 |
| ATL Europe (POA) Limited | Christchurch | 2019 |
| Atlante Projects Limited | London | 2012 |
| Atlantic Bay (Portstewart) Management Limited | Portstewart | 2000 |
| Atlantic Capital International Ltd | London | 2021 |
| Atlantic Circle Car Park Management Company Limited | Portstewart | 2000 |
| Atlantic Cove Portstewart Management Company Limited | Portstewart | 2002 |
| Atlantic Executive Limited | London | 2006 |
| Atlantic Financial Group Limited | Stafford | 2017 |
| Atlantic Fire & Security Ltd | Liverpool | 2010 |