OPINION: Clover Moore is seeking the intervention of the Governor of NSW, Marie Bashir, in a last-ditch bid to remain both the lord mayor and MP for Sydney.

She is asking the Governor to deny royal assent to a bill, passed last week, that bans dual roles. Moore is understandably angry about the new law, but her call on the Governor is misconceived and will prove futile.

Unpopular laws and community frustration with governments often lead to appeals to the Governor. Much of the final term of the previous Labor government was plagued by petitions, campaigns and bags of mail requesting the Governor to force an early election.

Such requests are never heeded, and neither should they be. They assume, incorrectly, that the Governor acts as a higher power in our system of government but, by longstanding convention, the Governor must act on the Premier's instructions.

Moore's plea is ironic, because it asks Bashir to ''defend democracy and refuse to give the bill assent''. In fact, little could be more dangerous to Australian democracy than for the Queen's unelected representative to veto a bill passed by the people's representatives in Parliament. Were the unthinkable to happen, it would revive the bitter controversies of the sacking of the Whitlam government by the governor-general, Sir John Kerr, in 1975.

Bashir will politely receive, and then rightly ignore, Moore's request. Her term as Governor has been marked by an acute understanding of her role's stringent constitutional limitations, and her duty is clear: she must act on the Premier's advice.

As Justice Ronald Wilson of the High Court said in 1982, the Queen's representatives ''may be described as a rubber stamp'' in the sense that they must accept whatever instructions they are given. Governors only have the rights to be consulted, to encourage and to warn.

It is only in the rarest and most exceptional of circumstances that a Governor can act against the advice of the Premier. Doing so is regarded as exercising a reserve power, and almost inevitably responds to, or gives rise to, a political crisis.

An example was in 1932, when the NSW governor, Sir Philip Game, sacked the premier, Jack Lang, due to Lang persisting with illegal conduct by refusing to make interest payments on the state's debts.

Moore's fight has also proved difficult on grounds of principle. She has a strong case that she has been an effective and able member of both State Parliament and the City of Sydney Council.

However, Moore's personal success cannot justify retaining a system that permits dual roles, if other general principles are of greater importance. Most other states prohibit a person from serving as a state member and a councillor. Commonwealth law bans state parliamentarians from standing for the Federal Parliament. The constitution may prohibit councillors from doing the same.

These laws reflect the principle that it is sensible to limit politicians to serving in only one elected body at a time. This acts as a check on their power, and recognises that the interests of different tiers of government can conflict so as to make it impossible for a member to assert the interests of both their state electorate and local council.

As an independent representative, and thus as someone who is never likely to serve in a state government, Moore has been able to sidestep these problems.

There are also questions as to whether elected officials have the capacity to simultaneously serve a state electorate and a local government area without one or the other losing out. Moore has done so ably and with enormous energy, but this does not mean that it is wise to permit people generally to do so.

Moore argues that the O'Farrell government's change is motivated by partisanship. After all, there is a good chance that, by taking her out of the state seat of Sydney, the electorate will be won by the Liberal Party at a byelection.

This is a comment on the politics of the change but it does not undermine the general principle at stake.

There are sound reasons of constitutional policy and practice that underpin why politicians should serve in only one level of government at a time.

George Williams is a Professor of Law at UNSW.

This opinion piece first appeared in The Sydney Morning Herald.