Legal moves which would end the practice of male heirs to the throne taking precedence over females are being held up by Australia, it has emerged.
The royal succession law must be pased in an identical form by all 16 Commonwealth realms who share the royal family - but Australia is holding up proceedings.
The six Australian states have to legislate before Canberra does, and Jim Wallace, deputy leader of the House of Lords, suggested a local election in South Australia may be responsible for the delay.
"To date, three states have enacted legislation, two have introduced legislation and one, South Australia, has yet to introduce legislation but it is in the middle of an election campaign," he said.
"The intention is that when all 16 realms have agreed or put in place the necessary legislation there will be a simultaneous order to give effect in each of the realms."
The rule change has already been agreed in principle by the prime ministers of the Commonwealth countries in Perth in 2011.
Civil servants delicately put together the bill and insisted on it being passed in identical form in each country, out of fear of different states ending up with different monarchs.
The change also limits the number of those in the line needing the monarch's permission to marry to six and allows anyone marrying a Roman Catholic to keep their place in the line of succession.
Catholics themselves remain excluded, however.
The Commonwealth realms are: Antigua and Barbuda, Australia, The Bahamas, Barbados, Belize, Britain, Canada, Grenada, Jamaica, New Zealand, Papua New Guinea, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Solomon Islands and Tuvalu.