It's time for me to return a favour. Way past time really, since the favour I am returning was gifted to me more than a decade ago.

And my act of reciprocation is not a lone one. It's a tiny part of the general exchange of ideas and advice among international conservatives, a new movement with the potential to be as significant as the coming together of international centre-left parties that followed the election of Bill Clinton in 1992.

Back in 1995, as I was heading off to work as John Major's adviser, I asked an old friend to visit London and give me the benefit of his thoughts. He had held senior jobs in the Reagan campaign and the Bush White House and had worked with some of America's best and toughest Republican political operatives. I was sure he would have some useful insights.

Once I'd taken him round a few Cabinet ministers and shown him some polling data I sat him down and asked for his view. What should we do? He opened not with an answer, but with his own question. “If you lose,” he asked, “what will you do?” I stumbled through my response, emphasising that deep change would be required, acknowledging new realities, moving towards voters and their views.

He looked at me and then asked another question. “And are you going to lose?” I'd seen the same polls he had. Of course we are going to lose,

I replied. This was his punchline: “Then what are you waiting for?”

This conversation stayed with me thoughout my time as an adviser. I never once doubted the need for profound change or the futility of waiting until later before beginning the process. I can't claim to have been particularly effective in achieving change, but my friend had ensured I never lost sight of the objective.

Now it's my turn. What do the Republicans do if they lose? They have to change, and change profoundly. They will have to move towards voters. And are they going to lose? It is extremely likely that they will. So what are they waiting for?

A new book, Comeback, by the conservative journalist and former Bush speechwriter David Frum begins with a bracing chapter entitled “Why We're Losing”. He records how the party is losing the middle middle class, previously staunchly Republican; how its big winners in the past - tax cuts, abortion, muscular foreign policy - have stopped working; and how the party is frozen in its response, quoting Reagan at every turn while refighting Richard Nixon's war against long-gone Sixties radicals. He shows how the tide is going out for the Republicans and will continue to do so even if it sneaks one more presidential victory. Unless it changes.

The significance of Comeback is not only its contents, it is also the identity of its author. Frum is one of the most important Republican intellectuals and very much part of its mainstream. Other conservatives (Andrew Sullivan, David Brooks) have called for change, but none with Frum's credentials on the Right. The publication of this new book is therefore a landmark.

The realisation that the Right has to change is taking hold in conservative parties all over the world. Modernisers in Australia, France, Denmark, Brazil, New Zealand, Canada, Sweden and, of course, Britain are among those most vigorously engaged in a debate about the common problems facing conservatives. Parties of the Left, based on universal ideas, have always co-operated. Conservatives parties, with their identity tied so closely to that of their nation, find it less easy to form international groupings.

But now they face a series of common challenges. The first is the political success of the Clinton-Blair Third Way. The instinct of conservatives was to dismiss this as a passing phase and a public relations con. Fifteen years later that is no longer possible. Across the world left-wing parties have accepted capitalism and moderated. This requires conservative parties to move towards the centre to compete.

Next, there is the waning appeal of small-government rhetoric. In the 1970s, speeches about government being the problem not the solution resonated. Now this language is much less potent politically. Government remains often inefficient and too large, but winning support to change it is harder. Conservatives need to show that they can run government, providing services, not merely talking about shrinking them. In Britain David Cameron has to persuade voters he can be trusted with the NHS; in order to win office Sweden's Fredrik Reinfeldt had to persuade voters to trust him on welfare; and Republican modernisers know they have to win over doubters on education.

This is linked to another issue - tax cuts. Always an automatic crowd-pleaser in the past, it isn't working quite as reliably as it used to. John Howard, for instance, lost in Australia despite his promises. In Britain, Conservative pledges have had mixed results. Voters don't believe them. And in America Frum notes a very good reason for this. Mostly it is not the middle class who gain, it is the very well-off.

If conservatives can no longer rely on the old tunes, they have to learn some new ones. All over the world conservatives are attempting to sell themselves as conservationist parties. On succeeding Mr Howard, almost the first act of new Australia's new conservative leader, Brendan Nelson, was to shift his party's position on climate change. Frum urges Republicans to abandon their old “read my lips, no new taxes” slogan and impose taxes on fossil fuel consumption.

And then there is cultural change. All over the world conservative parties have risked being left behind by the vast social changes of the past 40 years. Making peace with the Sixties is the hardest task, especially because while there have been good changes - equality for women, gay rights, racial tolerance - there have been bad ones too: marriage breakdown in particular.

Yet this hard task is essential. Nobody wants to vote for a party that angrily disapproves of how they live. That's the mistake the Left made as working-class people became wealthier and more mobile.

In the 1990s left-wing modernisers encouraged each other, sharing ideas and experiences, driving each other on, allowing the most popular leader at any given moment to help the others. Now modernisers on the Right realise that they must do the same.

There is, as someone once said, no turning back.

daniel.finkelstein@thetimes.co.uk

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