Simon Carr: Good news is the PM's back from China. Bad news is – no souvenirs

Sketch: He told an absent-minded Commons about how competitive devaluation would threaten global something or other

The Prime Minister has returned from China, and his first G20. He must have had a lovely time, everyone keen to see him, talk to him, photograph him. Flashbulbs everywhere, pretty girls, presidential jets, zillionaires, dictators with a billion-and-a-half subjects underneath them – and the finger food! – it can go to your head, all that.

The theatre of it, the celebrity, can give newcomers an entirely spurious sense that someone, somewhere, knows what's going to happen. That's the first step to administrative insanity. Anyway, he came back to give an account of his trip. He hadn't bought us anything. No souvenirs. No duty-free. No news. He told an absent-minded Commons about fiscal consolidation, imbalances, and how competitive devaluation would threaten global something or other. No one took much notice.

George Osborne must have had the best time of anyone. He took a big strategic decision two or three years ago, if you remember, that the deficit was the central political fact and it had to be dealt with aggressively. Gordon Brown found his only real pleasure in life by pointing out how isolated this position was. How lonely, how repudiated, how reviled Osborne was. Nobody agreed with him anywhere in the world... and now, quite suddenly it seems, everyone does. That, too, can go to one's head. We've yet to see whether these fellows are more psychologically resistant than their predecessors.

Harriet Harman was standing in for Ed Miliband, who's on paternity leave. It's the first decisive act of the Labour leadership, his first headline-grabbing public act – he has taken two weeks' holiday at the taxpayers' expense. Tony Blair's first weeks as leader were a little busier, weren't they?

Harriet put in a rousing, spirited, stupid response to Cameron. She felt it had all been a missed opportunity. She recommended a multilateral, supranational co-ordinated action plan to support growth. She suggested someone should have produced a global blueprint or a framework – Gordon Brown would have had one of them – "Britain needed to send a statesman but only sent a spectator!" she said to Labour cheers.

Cameron stood up and said lightly and in a way that would have made Joyce Grenfell smile, "Oh dear!" And then that it was "very nice to see the Hon lady back", and lots of "where she is right is". There were perfectly decent answers about protectionism and consolidation and all that communiqué litter.

PS: An oddity about the Speaker – he's starting to talk like Edward Heath. The vowels are elaborating. His grip on his apparatus in the Palace of Westminster has increased significantly – now we will see how psychologically resistant he is. A new way of speaking is usually a quick prelude to howling at the moon.

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