Political organisations
| Name | Type | Notes |
|---|---|---|
| Common Market Campaign | Pressure group | |
| Common Market Safeguards Committee | Pressure group | |
| Commonwealth | International body | |
| Commonwealth Institute | Miscellaneous | |
| Compass | Pressure group | |
| Confederation of British Industry | ||
| Conference of Churches of Christ | Miscellaneous | |
| Congregationalist | Religious | |
| Congregational Union of England and Wales | Religious | |
| Conservative and Unionist Organisation | Party group | |
| Conservative Association | Party group | |
| Conservative Cooperative Movement | Pressure group | |
| Conservatives for Europe | Party group | |
| Conservative Trade Union Association | Pressure group | |
| Cons Small Business Bureau | Party group | |
| Constitutional | Social club | |
| Co-operative movement | Party group | |
| Cork Defence Union | Pressure group | |
| Council of Agriculture | Pressure group | |
| Council of Auctioneers and Estate Agents | Miscellaneous |