MPs are holding their fourth day of debate on the Queen's speech, concentrating on constitutional affairs contained in the government's legislative programme for the year ahead.

The lack of bills on freedom of information, clearing the path for a referendum on proportional representation, and to reform the funding of political parties - all of which Labour promised in its election manifesto - will be highlighted by the Liberal Democrats.

The Lib Dems may even decide their non-appearance leaves the party no option but to vote with the Tories against the Queen's speech as a whole on Tuesday - though such a move would have as much to do with the wish to rebut allegations of being too cosy with Tony Blair.

Home Secretary Jack Straw will put the government's case for Lords reform

But the single constitutional measure that is expected to dominate this session of parliament is government's determination to remove the rights of hereditary peers - the majority of whom take the Tory whip - to sit and vote in the Lords.

The Tories have promised Labour a "bruising" contest on the issue.

Confirmation that the government's reforms will mean the Royal Family losing its historic right to sit and vote in parliament also give Conservatives ammunition to charge Labour with tampering with the monarchy.

The government says removing the hereditaries is "stage one" of its Lords reform intentions. A royal commission is to be set up to examine the options for "stage two".

The opposition's line is not to defend the principle of the hereditary peerage having a place in the legislature. Nor is it to deny the Lords could do with reforming.

Instead the Conservatives have insisted the government should make clear what the second chamber would be like at the end of the long reform process the government promises.

The Tories argue that because the interim House of Lords between stages one and two will be a wholly-appointed chamber, the government's reform will have the effect of turning it into a less democratic body - a "House of Cronies".

Added impetus

The hereditaries' removal from the upper chamber featured in Labour's election manifesto, and was given extra impetus at the end of the last session by the government's forced abandonment of its European Parliamentary Elections Bill.

The government needs to pass the Bill to fulfil its promise to hold next year's Euro-elections under proportional representation (PR).

But the legislation was dropped following Tory-led opposition to details of the precise system of PR preferred by the government.

Peers rejected the government's proposed "closed list" PR system five times.

The government is to re-introduced the Bill to the Commons on Wednesday with a guillotine motion to rush its passage through in one day. It will then be sent back to the Lords.