The Queen, pictured with the PM on a visit to Downing Street in June 2011 The Queen is expected to attend a cabinet meeting in Downing Street for the first time. Number 10 has said ministers will present her with a gift which they have bought to commemorate her Diamond Jubilee year.
It is believed to be the first time a monarch has attended cabinet since Queen Victoria's reign.
She is expected to sit between the PM and the foreign secretary for part of the regular meeting of top ministers.
While the Queen is head of state, her involvement in day-to-day political decisions is largely formal.
The prime minister visits her regularly for an audience where he updates her on events, while she is also expected to rubber-stamp ministerial decisions at meetings of the Privy Council.
The Queen plays a central ceremonial role in the state opening of Parliament, when she travels by ornate horse-drawn coach to the House of Lords to read out a speech prepared by ministers unveiling details of their legislative plans.
She also retains the power to appoint the prime minister.
The prime minister's spokesman said the Queen would spend about 30 minutes at the meeting, sitting between the PM and the foreign secretary.
The spokesman said he imagined she would speak, despite being described as an observer.
But Rodney Barker, professor of government at the London School of Economics, said the plan was "daft", because "it will mean potentially the Queen will know things she is not supposed to know and hear things she is not supposed to hear".
