This has been partly eroded by the spate of recent scandals at the DTLR, the IPR claims.
While stopping short of calling for a civil service act, the IPR is arguing for better self-regulation by government.
It is proposing a tighter definition of the role of special advisers so it is clear they are political appointees and may at no time instruct civil servants.
It also recommends changing their name to political adviser and offering them access to the pay structures and training that civil servants receive.
Opposition parties' policy advisers should also be given training in the civil service environment so that they are 'prepared for government', according to IPR head of policy Nigel O'Connor.
He added: 'All professional communicators ought to operate within clearly-defined roles, under systems of rules and reporting that are proportionate, and clear in their accountability.'