Civil servants are technically those people employed by the Crown.
In theory the Queen appoints all Government Ministers, though in practice the Prime Minister (and during the Coalition also the Deputy Prime Minister) appoints Ministers. This means that Government politicians are defined as Ministers of the Crown and civil servants are all those who are responsible to the Government.
So civil servants are those who work for:-
Civil Servants have a Code which specifies the standards to which they should keep, such as impartiality, and can complain to the Civil Service Commissioners if they are asked to breach this code.
They have a separate grading and pay structure.
There is a common process of entry and most civil servants are seen as having a general expertise in administration rather than a technical or professional expertise, which most people working in the NHS or for local government need, though they may develop a detailed knowledge of a particular policy area.
They are employed by the Government as a whole rather than by a particular department and so can be moved between organisations. This makes it easier to reorganise Government Departments.
Over 3000 civil servants are in the Senior Civil Service.
Senior Civil Servants work closely with Minister. Their job is to:
Departments keep in touch with each other to sort out problems that overlap their responsibilities.
Each Government Department is headed by a Permanent Secretary and the Cabinet Secretary is responsible for the civil service as a whole.