Leading Article: At last, the nation is offered a great promise

When in a season of political discord two parties come together in open agreement, it does not guarantee that they will talk sense, but it is a good omen. When they field, in Robert Maclennan and Robin Cook, two sensible and decent men, optimism grows. And the joint Labour and Liberal Democrat proposals for constitutional betterment did not disappoint.

A special merit was their modesty, and the fact that they still depend - in the case of plans for devolution and proportional representation - on popular approval through referenda. At last, it seems, the movement is under way to reform a constitution hardly less Venetian than when Tory Disraeli coined that phrase - disparagingly - a century and a half ago. We now have a prospect that within four or five years, perhaps even at the general election after next, voters will see a fairer representation of their choices than first-past-the-post offers. To many that reform would rank as the most far-reaching the next government could effect.

The report of the Lib-Lab consultative committee is far from perfect. It has several sore thumbs. One is reform of the Lords. The document funks what it is that a second chamber is intended to do. How far should an upper chamber explicitly be given a role of blocking, checking and where necessary kicking-for-touch? Only when we know what an upper house is for can we assess proposals for its composition - not that there are any in the Lib-Lab report. The hereditary peers disappear (except for those favoured few who are to be reincarnated as life peers) but how, and on what grounds, will they be replaced?

Perhaps there is method in ignoring the detail of Lords reform. This document embodies a huge commitment of Parliamentary time and political energy. A strong sense of priority among these reforms is vital, and not only to get them through the House of Commons. Any new government, whatever the size of its majority, has only a limited amount of political credit, which should be spent first on the big-picture changes. Giving the British people the option of radically changing the voting system must, in terms of its impact on our politics, be at or near the top of that list. There will never be final pre-referendum agreement on a single method of voting; the Reform Commission will have to struggle with details of Irish-style, German-style and other systems which are none of them perfect. But in the end it will give us a straight choice between a single more proportional system and the status quo. Reform may or may not happen; but that single agreement is a huge leap towards it.

Apart from full discussion of the Lords, the other yawning gap in the report concerns local government, and is all the more surprising given the long-term enthusiasm of the Liberal Democrats for genuine power-sharing, and indeed that party's current strength in the town and county halls. Is this dour realism on Labour's part? Is it embarrassment? Gordon Brown's proposals for budgetary control are deeply centralising and allow no room for local financial discretion, though even without new money there is much that local authorities could do freed of central constraint. But perhaps Labour is simply not prepared to see its little local embarrassments - its Doncasters and Liverpools - cut loose and allowed real freedom.

Still, it would be churlish to identify only the gaps without celebrating the commitments - for example, to the incorporation of the European Convention on Human Rights, and to a domestic apparatus helping citizens make use of its provisions. Recent discussion of privatisation as a way of securing improvements in London's Underground has once more focused attention on the dearth of city-wide democracy in the nation's capital. The report suggests the simple expedient of asking people whether they want an elected authority. It will be trickier than that. There is no easy way of identifying who the Londoners are who need to be invited to vote. Do they, for example, include the inhabitants of Carshalton and Uxbridge who, historically, have been most reluctant to be included?

But to pose that kind of question is to state the obvious: no reform is clean-limbed and simple. To seek to enact even half the packet of those displayed in this report would be to face down a mountain of opposition - Parliamentary opposition that will be furious, if not wholly cogent. To listen to Prime Minister Major is to be transported back to 1832 - since the country is so well governed, there is no possible justification for abolishing the constituency of Old Sarum. To listen to the more sophisticated Tory opponents of constitutional change is hardly more enlightening - according to David Willetts all manner of changes in our economic lives are natural and inevitable ... except modernisation of the way we are governed, which is somehow unnatural and to be resisted to the last ditch. The Tory position is, sad to report, little more than a defence of vested Tory interest. Under Conservative rule the British Constitution has been allowed to become unbalanced, disordered and, on occasion, a threat to liberty.

It may be that if the Tories lose the election some people (including some Labour front-benchers?) might in turn lose their enthusiasm for constitutional reform. Why do we need radical change when the system does after all allow alternation in power? But there's the real significance and challenge of yesterday's report. It is more than a here-today, gone-tomorrow manifesto commitment. Labour is promising something to Liberal Democrat voters and vice versa. They offer themselves to the voters as politicians groping beyond narrow party interest, experimenting with a more generous and plural way of holding power. It is a great promise, which deserves to awaken a prickle of interest in a sceptical nation.