| Seaboard Community Polytunnel Group Community Interest Company | Tain | 2022 |
| Seaborough Manor Limited | Yeovil | 1959 |
| Seabright Equestrian Limited | Leominster | 2016 |
| Seabuckthorn Scotland Community Interest Company | Edinburgh | 2018 |
| Seacliff Fishing Ltd | Kilkeel | 2014 |
| Seacombe Limited | London | 2008 |
| Seacon BEG Farm Limited | Ballymoney | 2017 |
| Seadog Shellfish Limited | Fakenham | 2013 |
| Seafarer Holdings Ltd | Brixham | 2025 |
| Seafarer Trawlers Ltd | Brixham | 2025 |
| Seafield Farm Ltd | Strathcarron | 2023 |
| Seafield Fishing Company Limited | | 2006 |
| Seafield Mussels Limited | Brae | 2015 |
| Seafield Park Limited | Nairnshire | 1996 |
| Seafood & EAT IT Fishing Limited | Penzance | 2016 |
| Seafood for Kngs Ltd | London | 2023 |
| Seaforde Estate Company Limited | | 2009 |
| Seaforth Mussels Limited | Isle Of Scalpay | 2015 |
| Seafresh N.I Ltd | Groomsport | 2019 |
| Seagenerate Ltd | Epsom Downs | 2021 |
| Seagrass Blue UK Ltd | Polegate | 2023 |
| Seagreens Harvesting Systems Ltd | Horsham | 2020 |
| Seagreens International Partnership Trustees Ltd | Horsham | 1989 |
| Seagrown Limited | Scarborough | 2018 |
| Seagrown Scotland Limited | Glasgow | 2025 |
| Seahorse Stud Ltd | Tarporley | 2022 |
| Seal Brook Livery Limited | Lullington | 2005 |
| Seal Forestry Limited | Perth | 2002 |
| Sealey Equine Limited | Blandford Forum | 2025 |
| Sealladh Meicli Blueberry Farm Limited | Ashford | 2026 |
| Sealladh NA Beinne Moire | Hs8 5Ss | 2005 |
| Sealmac Ltd | Inverness | 2021 |
| Sealord Ltd | London | 2018 |
| Sealskill Limited | Dorking | 1998 |
| Seamans Farms (Bintry) Limited | Dereham | 1977 |
| Sean Dennison | Orkney | 2024 |
| Sean Hardy Training Ltd | Hemel Hempstead | 2025 |
| Sean Porter (Padstow) Limited | Newquay | 2019 |
| Sean&Kathleen Kerr Ltd | Omagh | 2012 |
| Seanet Ltd | Dorking | 2011 |
| Seann Limited | | 2007 |
| Seapply Ltd | London | 2020 |
| Seaprime Fish Ltd | London | 2025 |
| Seaquest Excursions Ltd | Ringwood | 2022 |
| Seaqurefarming 1 Limited | Stornoway | 2024 |
| Seaqurefarming 2 Limited | Stornoway | 2024 |
| Seaqurefarming 3 Limited | Stornoway | 2024 |
| Seaqurefarming 4 Limited | Stornoway | 2024 |
| Seaqurefarming 5 Limited | Stornoway | 2024 |
| Seaqurefarming 6 Limited | Stornoway | 2025 |
| Searby Farming Company Limited | Brigg | 2001 |
| Searle & SON Ltd | Penzance | 2016 |
| Searle Agricultural Services Limited | Gloucester | 2015 |
| Searle's Forestry Limited | Thetford | 2025 |
| Searle's Holdings Limited | Thetford | 2005 |
| Sears Bros. Limited | March | 1944 |
| Seasalter (Walney) Limited | Barrow In Furness | 2000 |
| Seasalter Limited | Whitstable | 2023 |
| Seasalter Shellfish (Whitstable) Ltd | Whitstable | 1986 |
| Seascape Bloodstock Limited | Shaftesbury | 2021 |
| Season Crop (UK) Ltd | Bournemouth | 2016 |
| Season Well CIC | Leeds | 2021 |
| Seasonal Supplies Ltd | Bedford | 2019 |
| Seasoned and Saged Community Kitchen CIC | London | 2024 |
| Seasoned Logs Limited | Midhurst | 2014 |
| Seaswept Farm Limited | Paul | 2018 |
| Seat Hill | Carlisle | 2011 |
| Seatreefarms Limited | Surbiton | 2022 |
| Seaview Arboriculture Ltd | Southampton | 2022 |
| Seaview Equine Limited | Barrow In Furness | 2024 |
| Seaview Fishing Company (Peterhead) Limited | | 2003 |
| Seavive Projects Ltd | Bristol | 2025 |
| Seavox Ltd | Poole | 2024 |
| Seawater Solutions Ltd | Glasgow | 2018 |
| Seawave Leasing Limited | | 2003 |
| Seaweed Enterprises Limited | Glasgow | 2023 |
| Seaweed Farming Scotland Limited | Stirling | 2019 |
| Seaweed Generation Ltd | Falmouth | 2021 |
| Seaweed GUY CIC | Worthing | 2025 |
| Seaweed Services Ltd | Oban | 2023 |
| Seawell Grounds Limited | Towcester | 1981 |
| Seawild Ltd | Shoreham-By-Sea | 2020 |
| Seawise Solutions Ltd | Stromness | 2019 |
| Seazou Aquaculture Ltd | Narberth | 2024 |
| Seber Contracting Limited | Bedford | 2025 |
| Seckar KOI Ltd | Wakefield | 2026 |
| Second City Bulldogs Ltd | Sutton Coldfield | 2023 |
| Second Element Agriculture Ltd | Market Rasen | 2018 |
| Second Harvest Limited | Canterbury | 2024 |
| Second Meadows Livery Ltd | Ipswich | 2017 |
| Second Nature Tree Services Limited | Braintree | 2014 |
| Second Stellar Forestry (General Partner) Limited | Liverpool | 2010 |
| Second Twenty Ltd | Hatch Beauchamp | 2015 |
| Secret Equine Ltd | Newmarket | 2024 |
| Secret Garden Aquatics & Horticultural Supplies Ltd | Peterborough | 2018 |
| Secret Greenhouse Ltd | Southend-On-Sea | 2026 |
| Secrets of the Horse UK Limited | Bromsgrove | 2009 |
| Secure Generation Limited | Manchester | 2015 |
| Secure Storage Solutions (Birchwood) Limited | Ashford | 2020 |
| Secutus Consultancy Ltd | Peterhead | 2026 |