Have you noticed (I wrote in an early one of these columns in 2006) “how the Nokia 6310i mobile phone is refusing to die?”. I had just collected a secondhand handset of my own.

Well, it's still refusing to die. My new 6310i has just arrived. As-new, really: it's reconditioned. The 6310i was discontinued years ago. You'd recognise the model at once: longer, narrower, heavier than today's, with a classic, “Radio City” facia. And people still want them, because the keyboard is big, well-spaced and straightforward, the carcass is robust and the battery lasts about three days.

Only tarts and tea-boys want phones that double up as mini-music centres, games consoles, cameras and broadcasting studios. Serious people want a phone for making phone calls. So insistent has been the demand that there is now a company http://www.nokia6310i.co.uk/index.htm offering reconditioned 6310i handsets for about £100.

The model's survival is a great example of consumer resistance to unwanted “product development” by manufacturers. The consumer's problem has been that the main customer for phone handsets has been not the user, but the mobile networks that market them. Their interest lies in peddling devices that access new services and make new business.

I was telling my colleague Danny Finkelstein about my new theory that the free market doesn't work properly when the real customers are those who commission a product rather than those who use it. It is, for example, businesses, not the householder, that choose the courier service that makes you stay in all day in case it calls; it is insurance companies, not patients, that are are private medicine's real customers. “Ah,” said Danny, “this conundrum is well known to economists. They call it the Principal-Agent Problem. There are whole chapters in textbooks about it.”

I felt as proud as Molière's Bourgeois Gentleman, enchanted to discover from an expert that quite spontaneously he had been speaking something called “prose” all his life.

They've got it all wrong about the Clegg/Huhne contest for the Liberal Democrat leadership, narrowly won by Nick Clegg on Tuesday. Because Chris Huhne has chiselled features, a stubborn and hungry determination to be top dog and a ruthless instinct for headlines, while Mr Clegg has conducted his campaign with all the drive of one of those par-baked baps they sell in boutique cornershops, commentators are calling Mr Clegg bland and Mr Huhne focused.

The truth is otherwise. Mr Clegg is a serious man with rather coherent beliefs to which he is strongly committed. Mr Huhne is more opportunistic: driven yet directionless. Mr Clegg knows where he wants to go but has looked hesitant as to whether he's the man to lead the way.

But so was Moses. Were I a Lib-Dem I'd back Nick Clegg all the way. Cameron Conservatives are not as secure in their new 21st-century home as many assume, and I think Mr Clegg a potentially corner-turning leader for Liberal Democracy, a man of depth and calibre. But I think he needs a big, horrible fright in his life, and a vicious scrap.

Everyone is urging him to be bold. I would rather urge his enemies to be bold: test him; drag him out of the restaurants and into the trenches; scar him; wound him; it could be his burning bush.

As the year nears its close with a new Prime Minister test-driven, run-in and, from the look of him, near done-in, your diarist wrestles with a professional problem. I think Gordon Brown is mad.

But the trouble is, I said Tony Blair was mad, too. I said it for nearly ten years. Readers will surely begin to worry that it is I who am mad — or, worse, that I'm just a former Tory MP who thinks all Labour leaders are insane.

But with Mr Brown it shouts at you, doesn't it? The constant, mindless, repetition of comfort-blanket verbal formulae. The anger, the obstinacy — a man by turns bullying yet paralysed by indecision.

And those awful stories: fits of yelling at people, refusing to look at people, unpardonable rudeness to staff, fidgeting, nail-biting, afraid of letting go of anything, terrified of committing yet clinging with blind rigidity to commitments he does make. Then there's the (surely) telltale mistrust of all but a small circle of devotees...

I could go on. But I promise not to. Look, in return for easing up on this in 2008, can I just say one thing now about this madness stuff? With Tony Blair it was a metaphor. With Gordon Brown it's a diagnosis.

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