Queen Elizabeth II is donning an ermine robe and diamond-studded crown to announce the British government's plans for the coming year at the ceremonial State Opening of Parliament.

The speech is set to contain a mix of bread-and-butter legislative announcements and lofty aspirations from what Prime Minister David Cameron calls his "one-nation government" of compassionate conservatism.

Cameron says the most dramatic prison reforms since the 19th-century will feature in Wednesday's speech, which is written by the government but read out by the monarch from a gilded throne. Cameron says prison governors will be given more powers to ensure that the institutions are no longer "warehouses for criminals."

The speech is also expected to include measures to clamp down on extremist preachers that will be closely watched by free-speech groups.