| 12 Upperton Gardens Management Company Limited | Eastbourne | 1990 |
| 12 Victoria Park Freehold Limited | Dover | 2017 |
| 12 Walcot Buildings Management (Bath) Limited | Bath | 1986 |
| 12-14 Brudenell Road Management Company Limited | London | 2002 |
| 12-14 Folgate Limited | London | 1998 |
| 12-14 Hereford Road RTM Company Ltd | Portsmouth | 2015 |
| 12-30 Ltd | London | 2022 |
| 12/01 Solutions Limited | Thornton-Cleveleys | 2006 |
| 12/23 Architecture Design Ltd | Manchester | 2009 |
| 120 Bravington Road Limited | London | 1999 |
| 120+3 Limited | Derby | 2024 |
| 12001103 Ltd | Woodford Green | 2019 |
| 1202 Ltd | London | 2023 |
| 12026832 Limited | Cardiff | 2019 |
| 1203 Limited | Leamington Spa | 2024 |
| 1204 Design Ltd | London | 2025 |
| 1206 Partners Ltd | London | 2021 |
| 1207 Accountancy Ltd | Caterham | 2025 |
| 1207 Limited | London | 2022 |
| 120K Creative Ltd | London | 2020 |
| 121 Accountancy Partners Limited | Farnborough | 2011 |
| 121 Accounting Ltd | London | 2023 |
| 121 Beer Limited | Lutterworth | 2004 |
| 121 Branding Group Ltd | Macclesfield | 2021 |
| 121 Capital Advisory Limited | London | 2019 |
| 121 Captions Limited | Harrow | 2010 |
| 121 Cashiers Limited | Manchester | 2024 |
| 121 Company Formation Limited | London | 2011 |
| 121 Consultancy Services Limited | London | 2026 |
| 121 Consultant Limited | Ilford | 2010 |
| 121 Consultant Services Limited | Northallerton | 2017 |
| 121 Consulting Ltd | Aylesbury | 2024 |
| 121 Cranleigh Road Property Management Company Limited | Bournemouth | 2009 |
| 121 Cross Border Taxes Ltd | Bradford | 2026 |
| 121 Design and Build Ltd | Betchworth | 2019 |
| 121 Digital Marketing Ltd | Hull | 2023 |
| 121 Direct Mail Limited | Bredbury Stockport | 2005 |
| 121 Express Limited | Swindon | 2005 |
| 121 FS Ltd | Eastbourne | 2014 |
| 121 Group Services Ltd | Sittingbourne | 2023 |
| 121 HR Solutions Limited | Glasgow | 2010 |
| 121 Law Associates Ltd | Barking | 2012 |
| 121 Law Helpline Ltd | Datchet | 2025 |
| 121 Local Accounting Ltd | Coalville | 2013 |
| 121 Marketing Ltd | Birmingham | 2012 |
| 121 Osborne Road Management Limited | Tyne & Wear | 2003 |
| 121 Professional Services Limited | Northallerton | 2026 |
| 121 SC Limited | Aberdeen | 2003 |
| 121 Team Ltd | Ilkeston | 2024 |
| 121 UN Limited | Slough | 2020 |
| 121.COLLECTIVE Ltd | London | 2018 |
| 12103 Design Studio Ltd | London | 2020 |
| 1210S Design Ltd | Northampton | 2023 |
| 1211 Limited | London | 2012 |
| 1212 Process Solutions Ltd | Aberdeen | 2023 |
| 1212. COM Limited | London | 1998 |
| 121365 Limited | Worthing | 2021 |
| 1216 Advisory Services Limited | Oxford | 2014 |
| 1216 Business Services Limited | Keighley | 2020 |
| 1217 Edin Ltd. | Edinburgh | 2007 |
| 1217 Group Limited | Christchurch | 2023 |
| 121AVIATION Ltd | London | 2022 |
| 122 Consulting Ltd | Warrington | 2022 |
| 122 Mill Lane Management Company Limited | Lincoln | 2014 |
| 122 Services Ltd | London | 2026 |
| 1221 Ltd | Stanmore | 2015 |
| 1225 Taxis Ltd | Pathhead | 2013 |
| 1226 Accounting Ltd | Colchester | 2021 |
| 1226 Ltd | Accrington | 2021 |
| 1227 Business Limited | Salisbury | 2024 |
| 123 Accounting Solutions Limited | Manchester | 2008 |
| 123 Bedford Estates Ltd | Cardiff | 2025 |
| 123 Bookkeeping and Accountancy Limited | Ashford | 2023 |
| 123 Business Accounting Limited | London | 2018 |
| 123 Business Consultants and Recruitment Ltd | Rochester | 2023 |
| 123 Clarity Limited | Bristol | 2008 |
| 123 Cloud Accounting Ltd | East Leake | 2016 |
| 123 Dazzle Limited | East Grinstead | 2025 |
| 123 Domain Names Limited | Barrow-In-Furness | 2018 |
| 123 Domain Networks Ltd | Barrow-In-Furness | 2021 |
| 123 Drone Limited | Coventry | 2024 |
| 123 Easy Bookkeeping Services Limited | Basildon | 2010 |
| 123 Finance Ltd | High Wycombe | 2021 |
| 123 FS Limited | Chelmsford | 2017 |
| 123 Greg Ltd | Mansfield | 2024 |
| 123 Investments Limited | Leeds | 2008 |
| 123 Law Limited | Cardiff | 2021 |
| 123 Medical Ltd | Skelmersdale | 2019 |
| 123 Networks Limited | Barnet | 2009 |
| 123 People Development Ltd | Middlewich | 2014 |
| 123 Preston Road Limited | East Sussex | 1991 |
| 123 Project Management Ltd | Macclesfield | 2015 |
| 123 Promos Limited | Windsor | 2025 |
| 123 Strategy Limited | Rochester | 2022 |
| 123 Tax Ltd | Birmingham | 2018 |
| 123 Visuals Group Ltd | Bracknell | 2018 |
| 123 Yorkshire Accountants Ltd | Hudderfield | 2019 |
| 12345 Limited | Middlesex | 1999 |
| 123456789 Ltd | London | 2025 |
| 1237 Edin Ltd. | Rosewell | 2005 |