LONDON (Reuters) - The Commonwealth must do more to promote democracy and get tough on autocratic regimes, even if that means publicly "shaming" some of its members, said a report to be presented to its political leaders on Monday.

Many Commonwealth governments fail to "encourage, or even countenance, open political competition" and instead use state apparatus to repress dissent, said the report, commissioned by the club's policy think-tank and an electoral reform group.

In September, the 53-nation Commonwealth suspended Fiji after the leaders of a 2006 coup failed to make steps to return the country to democracy -- a rare sanction from the group which generally uses back-door diplomacy to persuade members to behave.

This subtle approach meant it was easier for "wily autocrats manoeuvre to deflect demands for reform", said the report, written by democracy experts from Britain, Ghana and Pakistan.

The Commonwealth -- mostly made up of former British colonies -- should publish regular democracy "health checks" for each member state, inviting the judiciary, media and non-governmental groups to contribute, it recommended.

Rather than just acting against countries that have undergone coups or obviously rigged elections, the Commonwealth should speak out against regimes which are more subtle in their repression.

"The Commonwealth can play an important role in monitoring such processes and shaming those governments who fail to respect the association's basic political values," said the report.

Promoting democracy "should not be just one among a number of Commonwealth objectives", it said. "It must become, and be recognised as, the defining characteristic of the association."

Commonwealth heads of state and government meet in Port of Spain, the capital of Trinidad and Tobago, from November 27 to November 29.