The Siberia pact is a chilling omen for Hague

Well, we missed it. While the Treaty of Novosibirsk was being hammered out, the British press corps was fast asleep. Round and round the parked prime ministerial aircraft walked Tony Blair and Paddy Ashdown, keeping carefully inside the red lines Russian immigration officials had painted on the tarmac.

In the early morning sunshine of Siberia, as the hacks snoozed through the stopover on the way back from Hong Kong, the two party leaders negotiated their subversive agreement. Its ultimate significance can only be judged years hence; but, unlikely as it may seem, Novosibirsk may take its modest place alongside Maastricht and Limehouse as the unlikely scene of a deal with huge consequences for British party politics.

It may not seem very much, the creation of a "joint cabinet committee" comprising six members of the governing party - Tony Blair, John Prescott, Gordon Brown, Jack Straw, Robin Cook and Ann Taylor - and five from the Liberal Democrats, including Ashdown, Menzies Campbell and Bob Maclennan. Whether it can reasonably be called a "cabinet" committee at all must be questionable. Is it, therefore, simply another talking shop, which will meet irregularly and go nowhere - a sop to the Lib Dems? Well the treaty-makers don't think so; and nor do the seething critics of the deal in both parties.

This agreement was not forced on the Prime Minister by the electors. It is not a case of politicians being pushed together in a shotgun alliance. On the face of it, Blair has opened the door of government to a party that received far fewer votes and seats than his, and agreed to discuss some of the most sensitive issues with it.

In fact, both Blair and Ashdown have taken a considerable risk. By including the Liberal Democrats in formal discussions on constitutional reform - continuing in government talks which began in opposition - Blair knows he will alienate some in his party. There are senior and vociferous, though so far private, critics of this whole business. Furthermore, Blair now exposes himself to a high-profile walkout if he reneges on any key part of the reform agenda - the Lib Dems could "do a Heseltine". One day, that might be damaging.

Ashdown, by contrast, risks incorporation. One of the most striking and repetitive themes of the new administration is the way in which it reaches out, and pulls possible critics or opponents into its embrace. Outspoken business leaders; newspaper owners; vocal and popular leftists (like Tony Banks); pundits; all have been offered chats, access and sometimes jobs.

Is this soft, dissent-calming embrace simply being extended to the Liberal Democrats, as the main non-Labour voice of radicalism, in order to defuse a possible source of embarrassing parliamentary opposition? Is it all about lulling them to sleep? Lib-Dem critics will say yes, of course; Mr Ashdown will be under pressure to demonstrate that his party is as wide-awake as ever, by encouraging it to attack Labour fiercely where the two do not agree.

These risks are hardly lessened by the fact that the two parties are going to be talking about policies they may quarrel over. Once the parties get down to the nitty-gritty of the membership and agenda for the commission on electoral reform, for instance, there is ample room for serious disagreement. Ditto Scotland, Lords reform and the Bill of Rights.

So why, given the risks, did the Siberian compact happen at all? Blair didn't have to do this. Ashdown has no pressing need to get into a row with some of his more traditional MPs and party officials.

One hesitates to say this. As a hack one is pre-programmed not even to think it. But one is driven to the inescapable conclusion that Blair and Ashdown meant, all along, exactly what they said; that their rhetoric about pluralism and a new style of British politics is sincere; and that they are long-term politicians in every sense.

That does not mean that cold political advantage is irrelevant. Far from it. Unless this is a false Siberian dawn (which I doubt), it is another stage in a reshaping of politics which is hugely in Blair's interests and in the interests of the reformist, pro-European and liberal politics which Ashdown also represents. As Peter Mandelson said in his book The Blair Revolution, members of the two parties "want to right the same wrongs, to end the same injustices" and their remaining differences "are becoming increasingly blurred".

Now we have, as of yesterday, a situation where those members share what is effectively a common leadership on some of the main questions of the day. Today, the constitution; tomorrow, surely, Europe too.

Just think what that means for yesterday's ruling party. Already some moderate Conservatives are in near-despair about their leadership and medium-term prospects. If William Hague is naive enough to continue to push the anti-Brussels, anti-reform agenda very hard, he will find people peeling away. Some such private discussions have already begun.

At that point, an invulnerable-seeming alliance of moderate and pro-European politicians, running right across from the old Tory left to the old Labour centre would start to emerge under Blair's leadership. Unless they changed their tune, the Conservatives would be in danger of shrivelling to a dissenting faction - a party of splenetic commentators - and the traditional markers of party politics would blur.

Whether, in the long term, that would be good for democracy, I rather doubt, though dissent and criticism will always bubble up somewhere. But it would clearly be good for New Labour, and the Liberal Democrats, and all their supporters in the country. At first sight, the Treaty of Novosibirsk looks innocuous and small. It is neither. Wise opposition MPs will sniff the wind from Siberia, and shiver.