| Sean Smyth Holdings Limited | Financial services | 2019 |
| Sean Webster Ltd | Arts & recreation | 2022 |
| Sean@Anchor Limited | Real estate | 2024 |
| Seanaptic Ltd | Information & communication | 2018 |
| Seanica Holdings Ltd | Real estate | 2018 |
| Seansammytonypam Limited | Health & social care | 2017 |
| Seansweeneybuild Ltd | Construction | 2025 |
| Seanykins Limited | Professional & scientific | 2019 |
| Search Convert Limited | Professional & scientific | 2016 |
| Search ME Recruitment Limited | Professional & scientific | 2016 |
| Searidge Properties Limited | Real estate | 2003 |
| Seascope Marine Services Ltd | Education | 2020 |
| Seascope Training Solutions Ltd | Education | 2013 |
| Seashore Creative Ltd | Wholesale & retail | 2026 |
| Season Healthcare Living Ltd | Hospitality | 2020 |
| Seasoned by DR Lola Ltd | Manufacturing | 2025 |
| Seatales Limited | Hospitality | 2026 |
| Seatoller Projects Limited | Real estate | 2023 |
| Seaverdy Care Limited | Health & social care | 2023 |
| Seaview Services Liverpool Ltd | Transport & logistics | 2012 |
| Seaweed Alchemy Ltd | Administrative & support | 2013 |
| Seawing Landguard International Limited | Transport & logistics | 1985 |
| SEB Housing Ltd | Real estate | 2025 |
| SEB Projects Limited | Construction | 2026 |
| Sebastian Tiling Services Ltd | Construction | 2026 |
| Sebytech Limited | Professional & scientific | 2018 |
| SEC Management Consultants NW Ltd | Professional & scientific | 2020 |
| Seceda Property Ltd | Real estate | 2025 |
| Second Chance Gifts and Recycling Liverpool Ltd | Wholesale & retail | 2015 |
| Second Chance L21 Ltd | Wholesale & retail | 2025 |
| Second Curve World Ltd | Arts & recreation | 2019 |
| Second Helping Limited | Professional & scientific | 2024 |
| Second Line Technologies Ltd | Wholesale & retail | 2026 |
| Second Sight Services Limited | Manufacturing | 2023 |
| Second Stellar Forestry (General Partner) Limited | Agriculture & fishing | 2010 |
| Secoya Ltd | Administrative & support | 2023 |
| Secret Beauty Room Walton Limited | Other services | 2019 |
| Secret Circus Events Ltd | Arts & recreation | 2018 |
| Secret Diamond Academy Limited | Education | 2021 |
| Secret Diamond Holdings Ltd | Other services | 2025 |
| Secret Sewing Rooms Limited | Wholesale & retail | 2021 |
| Sectorfuse Ltd | Information & communication | 2021 |
| Secura Facilities Limited | Administrative & support | 2021 |
| Securacar Ltd | Wholesale & retail | 2018 |
| Secure AV Ltd | Administrative & support | 2026 |
| Secure Bolts Ltd | Wholesale & retail | 2011 |
| Secure Care Connect Solutions Limited | Administrative & support | 2026 |
| Secure Claims Services Limited | Professional & scientific | 2017 |
| Secure Fencing Limited | Construction | 2011 |
| Secure Floor Coatings Ltd | Wholesale & retail | 2020 |
| Secure Holdings Investments Ltd | Financial services | 2014 |
| Secure Hotel Services Limited | Administrative & support | 2009 |
| Secure Install Limited | Administrative & support | 2018 |
| Secure Legal Services U.K Ltd | Administrative & support | 2017 |
| Secure Leisure Limited | Real estate | 2014 |
| Secure Marketing Services Ltd | Administrative & support | 2017 |
| Secure Medical Response Teams Ltd | Administrative & support | 2022 |
| Secure Peace of Mind Experts Ltd | Administrative & support | 2018 |
| Secure Store Containers Limited | Administrative & support | 2026 |
| Secure Substation Limited | Administrative & support | 2016 |
| Secure TOW Ltd | Wholesale & retail | 2020 |
| Secureabag Limited | Wholesale & retail | 2017 |
| Securebox Developments Ltd | Construction | 2023 |
| Securebuild & Hire Ltd | Construction | 2025 |
| Secured Doors Limited | Construction | 2012 |
| Securedigitali.Com Ltd | Information & communication | 1997 |
| Securetec Limited | Manufacturing | 2003 |
| Securevault Records Limited | Administrative & support | 2026 |
| Secureview Limited | Construction | 2010 |
| Securewatch Services Ltd | Administrative & support | 2024 |
| Security & FM Services Ltd | Administrative & support | 2024 |
| Security and Data Ltd | Construction | 2025 |
| Security Centres (Warrington) Ltd | Administrative & support | 2013 |
| Security Control Limited | Construction | 2008 |
| Security Labour Supplies Limited | Administrative & support | 2018 |
| Security NW Ltd | Other services | 2019 |
| Security, Stewarding & Training UK Limited | Administrative & support | 2016 |
| Secuura Ltd | Information & communication | 2025 |
| Seda Creative Ltd | Manufacturing | 2020 |
| Seddo Estates Limited | Real estate | 1996 |
| Sedem Properties Limited | Administrative & support | 2006 |
| Sedgcorr Property Limited | Real estate | 2008 |
| Sedgerton Limited | Professional & scientific | 2014 |
| Sedona Medical Limited | Other services | 2016 |
| Seduction Ltd | Wholesale & retail | 2025 |
| Sedulo Surveying Limited | Professional & scientific | 2020 |
| SEE It,Own IT. Ltd | Administrative & support | 2019 |
| SEE to a Star Limited | Education | 2007 |
| Seebj Ltd | Information & communication | 2025 |
| Seebohm Hill Ltd | Professional & scientific | 2013 |
| Seed and Sanctuary CIC | Education | 2025 |
| Seed Skills Ltd | Professional & scientific | 2025 |
| Seedlings Ltd | Education | 2025 |
| Seedotour Limited | Administrative & support | 2026 |
| Seegeetee Ltd | Professional & scientific | 2015 |
| Seel Hideout Ltd | Hospitality | 2013 |
| Seel ST Ltd | Real estate | 2026 |
| Seel Street Estates LLP | | 2012 |
| Seel Street Limited | Hospitality | 2022 |
| Seelgroup Limited | Hospitality | 2023 |