As Docklands barricades come down and the winking lights of departing foreign leaders' jets fade into the dusk sky, Gordon Brown must move from one world back into another - ours.

The world where he has been this week is the one in which he thrives. With dissent distanced by steel fences and popular disquiet only a sigh borne in on the air-conditioning ducts, in an artificial space where bureaucrats bark, sherpas sherp, coffee trays tinkle, the murmur of an interpreters' pulseless prose is just audible through foreign counterparts' headphones, and the only fizz is from a discreetly placed bottle of aerated water, Mr Brown crawls from the muck of British reality and spreads his dragonfly wings.

Here in this ultimate bubble are lists. Here are numbers. Here are abstract nouns. Here are moral imperatives prioritised, one, two, three. Here our Prime Minister feels comfortable. Here 99.9 per cent of the rest of the electorate would recoil helpless, repelled by the unreality.

As a crop of commentary has pointed out, this has probably been the happiest week of Mr Brown's life so far. The interesting question, however, is whether future commentary will be able to dispense with the words “so far”.

For now, I would be astonished if the week of the London summit does not lend Labour an immediate upturn in the opinion polls. It never was Mr Brown's personal charm, oratory or even argument that gave him what positive grip he has on the national imagination.

It was the idea that he was a dogged kind of bloke who could dig in his heels and bang heads together. The week behind us has played precisely to this strength.

If summoning to London virtually the entire economic leadership of the planet, kicking away the cynics' doubts, blocking his ears to the sneers of the media, gripping grimly to the arm of a popular new US president and making him a stage prop for Mr Brown's own show, and coming out of it all with - if not the New World Order he claims - then at least a few credible tweaks to the existing order... if none of this boosts Mr Brown, then all is truly lost. It's surely worth a bounce.

Mr Brown bounces well. Gravity, however, has a habit of bringing him back down. It is to gravity that the Tories must look, and it is about the existence of that highly inconvenient law of nature that they must keep reminding the rest of Britain.

First, though, good manners. It would be graceless not to acknowledge the Prime Minister's accomplishment in London this week. Hopefully David Cameron will not make such a mistake. “Shucks, he got away with it” will not do.

The Tories must see - or if not, at least see that the voters believe - that something good has happened. By dint of Mr Brown's own bull-headed insistence, the G20 leaders gathered for a summit from which can be distilled, if not a durable list of hard-edged plans for action, then perhaps at least an infectious spirit of co-operation and hope.

Hope counts. Mr Brown's critics will point out that in substance he hardly got what he wanted: a few weeks ago he was pushing for the announcement of a huge new global fiscal stimulus while Angela Merkel and Nicolas Sarkozy were rejecting the idea in favour of more co-ordinated financial regulation.

They prevailed. The idea of a huge new stimulus was dropped, and proposals for better regulation pushed forward. But if the argument didn't really go Mr Brown's way, the symbolism did. And it happened in London, and he - and we - should be proud of that. In a psychological climate where mood swings create and destroy jobs, savings and profits, symbolism can be critical.

So although this weekend's newspapers, and the deeper analysis that will emerge as the results are digested, will begin to unpick some of what this gathering has seemed to achieve, let's give it - and Mr Brown - their due. When uncoordination, panic and despair have bedevilled economics and politics all over the world, Mr Brown achieved in London a grand international gesture of solid, unflustered co-operation. Two cheers for the appearance, whatever the reality.

But for Mr Brown this weekend, the few miles back from the ExCeL centre to Downing Street must be like the thousands traversed back from a lovely fly-now-pay-later foreign holiday. The sun has shone, the sea has sparkled, food came on trays borne by waiters, and it's all been grand.

Now come the reality and the drizzle. The front door will barely open because of the bills accumulating on the doormat, weeds have overtaken the lawn, and a pile of neglected washing-up is sprouting mould in the sink.

This is Britain 2009 - and it is the Conservative Party's duty to bring Mr Brown back down to earth here. And what Mr Cameron, George Osborne and Kenneth Clarke need to make us see is that the end of the global economic downturn was never in doubt. Those of us who stubbornly refused to accept that there had been an end to boom and bust did not, by insisting that the boom would end, mean that the ensuing bust never would.

The natural companions of the new Labour ignoramuses who thought the boom was perpetual are the old Labour ignoramuses who gleefully prophesy the end of capitalism, and perpetual bust.

The rest of us believe in cycles. And as markets recover and neighbours and competitors move back into the sun, what we British must focus on is how our own country will cope. If I am right, and if the Tories are right, our own recovery is distinguishable from the global one: ours, although finally inevitable, will be beset with local difficulties. And many of them are of Mr Brown's making.

“You've saved the world, Gordon; but what about Rotherham”? Does this sound churlish? It shouldn't be understood that way. The Prime Minister of the United Kingdom commands a second-rank power whose ability to mould a world economic order, although not derisory, is very limited. His ability to wreck his own country's finances, however, is awesome. Labour is wrecking Britain's finances.

It is Mr Cameron's duty to make sure that, here at home, this truth is acknowledged as central - not just an embarrassing footnote to a successful G20 summit. It is the summit that should, in the end, prove the footnote.

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