Constitutional reforms will enshrine right of MPs to vote on going to war

Some of the most sweeping changes to the powers of Parliament are to be announced today, including a guarantee that MPs will have a vote before British troops can go to war.

Gordon Brown, the Prime Minister, will also reinforce the reforms to the British constitution in a speech on liberty. He will announce a consultation on easing restrictions on demonstrations near Parliament, which have enraged civil liberties groups and seen protesters arrested and prosecuted for reading out the names of the dead in Iraq.

The package of reforms – described by ministers as a new constitutional settlement for the 21st century – is regarded by the Prime Minister as his break with the Blair administration and is intended to bury the claims that he is a centralising "control freak".

Jack Straw, the Secretary of State for Justice, will announce that the Government is surrendering the right to send British troops into battle without a vote in Parliament, a move fiercely resisted by Tony Blair.

Mr Brown's comprehensive package of proposals will raise the long-term prospect of Britain having a written constitution for the first time. Mr Straw won Cabinet approval for the plans on Tuesday. They closely follow the green paper, The Governance of Britain, published in July as one of the first major acts of Mr Brown's premiership.

It will give Parliament oversight of the security and intelligence services by creating a Commons select committee to replace the special committee which is answerable directly to the Prime Minister. It will also surrender the Prime Minister's power to choose bishops and give MPs the chance to endorse the appointment of senior judges.

Reform of the House of Lords, an issue which has dogged Labour for more than a decade, is also foreshadowed in the package. The Government has secured cross-party support for a largely elected upper chamber with 80 per cent elected members and 20 per cent appointed by political leaders.

However, the tricky issue of how to deal with the existing life peers and the remaining 92 hereditary peers has still to be resolved, possibly by allowing them to carry on for more than a decade.

The Government has compared its reforms to the Magna Carta, traditionally regarded as the bedrock of personal liberties in Britain, and the Glorious Revolution of 1688 that brought in the era of parliamentary democracy in which no monarch could wield absolute power.