The government will unveil its plans later to replace the House of Lords with an elected second chamber.

There will be a draft bill included in a White Paper for a house of 300 members serving 15-year terms, with one third of them elected by proportional representation every five years.

Deputy Prime Minister Nick Clegg will set out a series of options in an attempt to secure consensus for change.

But the plans are expected to face strong opposition from peers and MPs.

Many options

In the coalition agreement, the government promised to bring forward proposals to reform the House of Lords.

On Tuesday it will fulfil that promise, at least up to a point.

The draft bill will be tucked discreetly at the back of a White Paper containing as many options as there are proposals.

The government will not specify whether the whole chamber should be elected or whether some - 20% - should be appointed.

It will not specify the chamber's name, which form of PR should be used for the elections, the size of the multi-member constituencies and - most contentious of all - what should happen to the 800-odd existing peers.

One option is for all but 200 to be expelled immediately, with the survivors elected from among their own number.

Another would see their expulsion phased in more gradually with a third nominated out as a third elected come in.

Another option would see them all staying on until 2025, at least those who survived.

Early fight

Ministers had been hoping to come up with something rather more specific but the plans changed in recent weeks.

First the alternative vote referendum was overwhelmingly defeated and Mr Clegg is keen to avoid a reputation as a man obsessed with tilting at constitutional windmills when the rest of the country is worried about the economy.

Second, a strategic decision has been taken to try to seek some kind of consensus, optimistic though this may be.

By listing options rather than a prescriptive plan, Mr Clegg hopes to avoid provoking an early fight with peers.

And by offering them the chance to stay on in the reformed second chamber, he hopes to buy off some who are more interested keeping their backside on a red bench than the constitutional niceties of reform.

All the detail will now be considered by a joint committee of both houses of Parliament that will be asked to report by next February.

Only once that committee has reported will we see just how serious the government is about reform.

Timetable doubts

In theory the government would like to be able to respond to the committee by the spring so it is in a position to put forward a proper, all-singing, all-dancing bill in the next Queen's speech in May 2012.

The bill would go through Parliament in the back end of 2012 and the beginning of 2013 so that there would be enough time to get everything ready for the first Lords elections on the same day as the general election in 2015.

That, at least, is the optimistic scenario. But the prospects for delay and parliamentary trench warfare are huge.

For a start, the government may ask the joint committee to report by next February but that may not happen.

The committee may decide to take more time. Committees do that. The May 2012 deadline for a proper bill may, as a result, be missed.

The bill may make such slow progress that it clogs up all other parliamentary business and has to be abandoned.

It might eventually get through but too late for arrangements to be made for the 2015 elections.

Bad omens

Opponents of reform are already getting organised, sending letters to MPs and forging cross-party alliances.

The three main party leaderships may all be signed up to some kind of elected second chamber but their parliamentary parties are much less keen.

Many peers oppose an elected second chamber because they fear it will politicise their house, depriving it of independent expertise, knowledge and wisdom, and filling it instead with party apparatchiks.

Ed Miliband may favour a wholly elected second chamber but many of his Labour peers are as opposed to reform as their Conservative colleagues.

And many MPs oppose an elected second chamber because they fear it will be more assertive with its new found elective legitimacy, and challenge the supremacy of the House of Commons.

Already the search is on for the new Michael Foot and Enoch Powell, the two MPs who formed a cross-party alliance to head off an elected Lords in the late 1960s.

The likelihood is that if the government wants to get this through, it will probably at some stage have to use the Parliament Acts to override the Lords and force the changes through against their will, something that has only been done four times in the last century.

Ultimately, the question for the government is how much political capital it is prepared to spend on something that a Liberal government first promised in the pre-amble of the Parliament Act of 1911.

The omens for a speedy result are not good.