Well of course Nick's a bit grumpy. He's probably suffering from a touch of 'Paul McCartney Syndrome'.

Imagine this. You're the best paid actor on US televison - despite the considerable handicap that you are British and play an American character. You are also one of the best selling novelists in France. An excellent sportsman, you were a Cambridge rowing blue. Last year, you played piano on Meatloaf's new album, this year you've launched your own blues guitar album, to wide critical aclaim. You are, by anyone's standards, a high achiever.

And yet, as you lie awake at night staring at the ceiling, you know back at home, everyone still thinks of you as the less talented half of Fry and Laurie. And that must hurt. And it makes you just a tad of a grump.

This is what a very talented planner called James Hillhouse once described to me as 'Paul McCartney syndrome'. Sure you wrote 'Yesterday' and 'the Long and Winding Road'; and of course you were part of the greatest band the world has ever seen. But you're still thought of as the slightly less talented half of that songwriting team and get the Frog Chorus hung round your neck at every turn. And despite the multiple nice houses and fast cars, and even though you know you're still one of the luckiest people alive - it still rankles.

Of course its even worse if - like Hugh Laurie and Paul McCartney, you have similar backgrounds and experience as your 'other half '. Which brings us on to Nick.

People keep saying Nick looks tired, that he's struggling with the pace, that's he's disenchanted with leadership. All of which I think is nonsense. But I do think he's a bit grumpy. Here's why.

Nick was elected Leader of our party in his early forties - and led us into government for the first time in 80 odd years. While there, in the first year, we've introduced the Pupil Premium, a Freedom Act and we're weeks away from a referendum on a major step change in the way our government is elected. Lib Dems litter the cabinet and every government department. By any standards, Nick Clegg has achieved an awful lot.

And yet. And yet..

Every day he must stare at David Cameron - a man elected to lead his party at the same age he was. A man in the top job, not the deputy top job. A man who's riding high in the opinion polls on his performance, while you get the blame for everything that goes wrong. And there's only one of you getting dog poo shoved though your letterbox.

Despite everything he's managed to achieve, that must be hard. And Nick wouldn't be human if it didn't hurt, nor if, try as he might, once in a while he let it show.

He's suffering from Paul McCartney syndrome.