| Seaborne & Partners Limited | Administrative & support | 2020 |
| Seachange Group Ltd | Information & communication | 2025 |
| Seacon Environment Ltd | Construction | 2009 |
| Seacroft Approach Limited | Real estate | 2017 |
| Seacroft Chair Works Limited | Water & waste | 1957 |
| Seacroft Fast Food Ltd | Hospitality | 2024 |
| Seafood Boil Specialist Ltd | Hospitality | 2024 |
| Seaford Funding Limited | Financial services | 1999 |
| Seaforth Trades Ltd | Administrative & support | 2024 |
| Seagulls RE - USE Limited | Water & waste | 2004 |
| Seaham Action Workshops 2010 Ltd | Administrative & support | 1983 |
| Seahouses Bidco Limited | Financial services | 2025 |
| Seahouses Midco Limited | Financial services | 2025 |
| Seahouses Topco Limited | Financial services | 2025 |
| Seal Cleaners Limited | Administrative & support | 2002 |
| Seal Metal Recycling Ltd | Water & waste | 2007 |
| Sealgull Properties Limited | Real estate | 2025 |
| Sealife Crewing Services Limited | Administrative & support | 1990 |
| Sealineleeds Limited | Hospitality | 2026 |
| Seam (Yorkshire) Limited | Real estate | 2016 |
| Seamen UK Ltd | Wholesale & retail | 2020 |
| Seamless Market Entry Advisory Limited | Professional & scientific | 2026 |
| Sean Mchale Coaching Ltd | Arts & recreation | 2024 |
| Sean Mcmahon Interiors Limited | Professional & scientific | 2022 |
| Seanor Investments Ltd | Real estate | 2026 |
| Search Engine Wizard Limited | Information & communication | 2026 |
| Search Estate Agents Ltd | Real estate | 2020 |
| Search Focused Limited | Professional & scientific | 2017 |
| Search Group Holdings Limited | Professional & scientific | 2008 |
| Search Park Limited | Other services | 2023 |
| Search Point Ltd | Administrative & support | 2019 |
| SEARCH4PARTS Ltd | Manufacturing | 2021 |
| Searchagain Limited | Real estate | 2013 |
| Seascale Chem Ltd | Wholesale & retail | 2018 |
| SEASCAPE789 Limited | Information & communication | 2015 |
| Seaside Cottages Limited | Real estate | 2021 |
| Seaside Holiday Lets Limited | Real estate | 2021 |
| Seaside Trading Services Ltd | Wholesale & retail | 2012 |
| Seaskin Limited | Wholesale & retail | 2017 |
| Season Well CIC | Agriculture & fishing | 2021 |
| Seasonal Entertainments Ltd | Other services | 2021 |
| Seasoncare Ltd | Construction | 2023 |
| Seasons Soft Drinks Limited | Manufacturing | 1997 |
| SEB DLS2 Ltd | Transport & logistics | 2025 |
| SEB Electrics Ltd | Manufacturing | 2018 |
| Seba (UK) Limited | Construction | 2009 |
| Sebar Properties Limited | Real estate | 2024 |
| Sebastian Davies Limited | Information & communication | 2018 |
| Sebastian Hankin Broadcast Limited | Information & communication | 2019 |
| Sebastian Heath Solutions Ltd | Professional & scientific | 2015 |
| Sebys Cleaning Ltd | Administrative & support | 2025 |
| SEC Audiology Limited | Health & social care | 2026 |
| SEC Highway Lighting (NO.2) Limited | Financial services | 2003 |
| SEC Highway Lighting (NO.3) Limited | Financial services | 2005 |
| SEC Highway Lighting (NO.4) Limited | Administrative & support | 2006 |
| SEC Lighting Services Trading Limited | Construction | 1996 |
| SEC Management Limited | Hospitality | 2014 |
| SEC365 Limited | Information & communication | 2020 |
| Second Avenue Productions (UK) Ltd | Information & communication | 2014 |
| Second Chance Dog Rescue CIC | Other services | 2021 |
| Second Mouse Holdings Limited | Hospitality | 2023 |
| Second Rodeo Limited | Information & communication | 2024 |
| Second Summer Ltd | Wholesale & retail | 2021 |
| Second to None Limited | Professional & scientific | 2008 |
| Second Wave Ltd | Professional & scientific | 2022 |
| Secondhandracking .COM Limited | Administrative & support | 2010 |
| Secondhandracking.Com Holdings Limited | Financial services | 2025 |
| Secondnature International Ltd | Administrative & support | 2015 |
| Secondrain Limited | Wholesale & retail | 2024 |
| Secops Services Ltd | Administrative & support | 2026 |
| Secret Code Limited | Administrative & support | 2007 |
| Secret Garden Cattery Ltd | Other services | 2017 |
| Secret Garden Leyburn Ltd | Real estate | 2021 |
| Secret Sky Cafe Limited | Hospitality | 2024 |
| Secret Smile Photography Ltd | Professional & scientific | 2010 |
| Sectr Partners Limited | Administrative & support | 2023 |
| SECUR3 Electrical Ltd | Construction | 2020 |
| Secura Management Limited | Administrative & support | 2004 |
| Secure 80 Ltd | Professional & scientific | 2019 |
| Secure Buildings Ltd | Construction | 2025 |
| Secure Industrial Doors Limited | Professional & scientific | 2007 |
| Secure Micro Solutions Limited | Wholesale & retail | 2011 |
| Secure Perimeter Fencing Solutions Ltd | Administrative & support | 2025 |
| Secure Scale Systems Ltd | Information & communication | 2025 |
| Secure Track UK Ltd | Real estate | 2024 |
| Secure Watch Security Limited | Financial services | 2026 |
| Secure Windows Ltd | Construction | 2026 |
| Secured Nation Staffing Solutions Ltd | Administrative & support | 2025 |
| Securelion Services Group Ltd | Administrative & support | 2022 |
| Secureme Limited | Information & communication | 2019 |
| Securenet OPS Limited | Administrative & support | 2025 |
| Securerail Limited | Manufacturing | 1996 |
| Securetech Consultancy Limited | Information & communication | 2023 |
| Securetime Systems Limited | Administrative & support | 2008 |
| Securi-Plex Limited | Administrative & support | 1988 |
| Securiclick Limited | Information & communication | 1999 |
| Securilix Ltd | Information & communication | 2024 |
| Securiscope Services Ltd | Public administration | 2021 |
| Securisure Security Services Ltd | Construction | 2026 |
| Security Contractors Yorkshire Ltd | Administrative & support | 2023 |