| 3MB Consultancy Ltd | Rugby | 2023 |
| 3MC Design and Digital Consulting Ltd | Bristol | 2025 |
| 3MC Holdings Ltd | Sheffield | 2024 |
| 3MCEWAN Ltd | Deal | 2026 |
| 3ME Design Ltd | Bristol | 2019 |
| 3MG Biomedical Ltd | London | 2025 |
| 3MG Limited | Purley | 2006 |
| 3MH Limited | Harpenden | 2021 |
| 3MIL Limited | New Malden | 2007 |
| 3MJ Consulting Ltd | Bromsgrove | 2016 |
| 3ML Management Services Ltd | Aberdeen | 2023 |
| 3MMM Accountancy Services Ltd | Leeds | 2015 |
| 3MN Ltd | Watford | 2024 |
| 3MR Enterprise Ltd | Chelmsford | 2025 |
| 3MSCOTLAND Ltd | Glasgow | 2019 |
| 3MSE Ltd | London | 2014 |
| 3MT Limited | Bangor | 2020 |
| 3N Consulting Limited | Benfleet | 2014 |
| 3N Diagnostics Limited | Belfast | 2013 |
| 3N Strategy Limited | London | 2012 |
| 3NE Ltd | Lisburn | 2015 |
| 3NIO Ltd | Barnsley | 2017 |
| 3NITE Limited | Redhill | 2023 |
| 3NT Ltd | Kettering | 2017 |
| 3NTROPY Ltd | London | 2026 |
| 3NVISION Consultancy Ltd | Rochester | 2025 |
| 3OCTO Project Ltd | Buckingham | 2023 |
| 3OH Ltd | London | 2025 |
| 3P Accountants Limited | Billericay | 2023 |
| 3P Consulting Ltd | Lytham St. Annes | 2025 |
| 3P Consulting Solutions Limited | Verwood | 2015 |
| 3P Global Services Ltd | Henley-On-Thames | 2016 |
| 3P Ministries | Carlisle | 2002 |
| 3P Sense Limited | London | 2016 |
| 3P Strategy Ltd | Shipston-On-Stour | 2017 |
| 3P'S Publishing Limited | Bristol | 1987 |
| 3PAY (Funders) Ltd | London | 2023 |
| 3PAY Collections Ltd | London | 2022 |
| 3PB Management Services Limited | London | 2013 |
| 3PCORE Ltd | London | 2025 |
| 3PCUBED Ltd | Rowlands Gill | 2020 |
| 3PEAKS Solutions Limited | Cheshire | 1999 |
| 3PLEA Ltd | Billericay | 2021 |
| 3PM Group Ltd | Fareham | 2016 |
| 3PN Ltd | Cheltenham | 2021 |
| 3POINT1 Consulting Ltd | London | 2020 |
| 3POINT1 Developments Ltd | London | 2022 |
| 3POLIS Limited | London | 2010 |
| 3PRM Ltd | Ryton On Dunsmore | 2017 |
| 3PROSONLINE Ltd | Bournemouth | 2021 |
| 3PS Chauffeur and Protection Services Limited | Crawley | 2014 |
| 3PTI Limited | Mildenhall | 2025 |
| 3PX Ltd | London | 2019 |
| 3Q (UK) Limited | London | 2000 |
| 3Q Consulting Ltd | Manchester | 2024 |
| 3Q Limited | London | 2009 |
| 3Q Scientific Limited | Neath | 2014 |
| 3QETC Ltd | London | 2021 |
| 3QHUB Ltd | Derbyshire | 2022 |
| 3QKC Services Limited | London | 2025 |
| 3QUENCY Limited | London | 2022 |
| 3QUK Limited | Newcastle | 2017 |
| 3R Equipment Group Ltd | Edinburgh | 2024 |
| 3R Features Limited | London | 2018 |
| 3R Insights Ltd | London | 2016 |
| 3R Management Limited | Croydon | 2014 |
| 3R Partners (Investments) Limited | Watford | 2013 |
| 3R Renewables Ltd | Hawick | 2006 |
| 3R Studios Ltd | London | 2020 |
| 3R Surveying Ltd | Glasgow | 2021 |
| 3R'S Consultancy Limited | Accrington | 2022 |
| 3R2 Ltd | Mold | 2025 |
| 3RAN Services (Wembley) Ltd | North Wembley | 2011 |
| 3RD Bridge Architects Ltd | Stockport | 2023 |
| 3RD Dimension CAD Ltd | West Malling | 2017 |
| 3RD Dimension Design Limited | Chelmsford | 2024 |
| 3RD Dimension Ltd | Birmingham | 2019 |
| 3RD EYE Accountax Ltd | Manchester | 2017 |
| 3RD EYE Bookkeeping & Payroll Ltd | Manchester | 2023 |
| 3RD Floor Media Ltd | London | 2023 |
| 3RD Generation Communication Limited | London | 2000 |
| 3RD Mile Ltd | Paisley | 2025 |
| 3RD Party Collateral Services Limited | Hollinwood | 2013 |
| 3RD Party Wall Ltd | London | 2023 |
| 3RD Project Design Limited | Southampton | 2011 |
| 3RD Sector Consultancy Ltd | London | 2023 |
| 3RD Sector Finance Limited | Belfast | 2016 |
| 3RD Sector Solutions Limited | Altrincham | 2018 |
| 3RD Vision Business Consultancy UK Ltd | Reading | 2019 |
| 3RD Way Solutions Limited | Evesham | 2013 |
| 3RDIMENSION CAD Services Limited | Derby | 2021 |
| 3RDTEAMCONSULTANCY Ltd | Liverpool | 2024 |
| 3RE Planning Limited | York | 2013 |
| 3RE UK (Dama) Limited | London | 2024 |
| 3RE UK (London JV) Limited | London | 2024 |
| 3RM Associates Ltd | Wakefield | 2013 |
| 3ROCKAR Ltd | London | 2013 |
| 3RT Smart Gold Holdings Ltd | London | 2022 |
| 3S (MK) Ltd | Mount Farm | 2020 |
| 3S Accountancy Limited | Darlington | 2003 |