Is art sacred or should you draw penises all over it and smash it?

Grayson Perry does that in his new series, Grayson Perry: Who Are You? (Channel 4). He also mocks Chris Huhne about prison and wonders whether converting to Islam stops you desiring 20 pairs of shoes.

And what a great programme it was: just one tiny hour but fizzing with ideas and irreverence and thought, all punctuated by Grayson Perry's dirty laughter.

This was the first in a new series examining identity. Who are we? How do we construct our identity and what forces are trying to dismantle it?

To explore this, Grayson met people from different classes, races and genders who had one thing uniting them: they were all at a crossroads in their lives. He discussed their sense of identity then created portraits of them, all of which are now on display in the National Portrait Gallery.

Portraiture was the best tactic for this as it makes the artist 'part psychologist and part detective', said Grayson, setting out to capture 'something a thousand selfies never could.'

And it made him laugh to think his portraits of the odd and marginalised and eccentric would be displayed beside those of the haughty, old, rich, white people who comprise most of the Gallery's subjects.

His first candidate was Chris Huhne, who represents what Grayson calls the Default Man: white, middle-aged, heterosexual and privileged. He met Huhne the night before his sentencing, then again on his release from prison. Had his identity taken a battering now he was an ex-con?

No, he insisted, ever the politician, skirting the difficult question. Grayson prodded him as they breakfasted in a motorway cafe near the jail, but Huhne smirked and claimed he was still the same person (translation: I have learned nothing!).

Grayson was amazed at his conviction (pardon the pun) that his character remained untouched. Can nothing dent the awful self-importance of Default Man?

The mask almost slipped when Grayson jokingly asked him to show his prison tag, or 'the Hackney Rolex'. Huhne forced a smile and refused, but the discomfort was evident.

His resultant portrait was no prim painting but a ceramic pot decorated with penises and speed cameras. Grayson smashed it then glued it back together, leaving the cracks very evident.

He then ventured to the 'lower slopes of celebrity culture' to meet former X-Factor contestant, Rylan Clark. Rylan was tanned and styled yet utterly lacking in confidence. His public persona was alien to him, but he needed it to make a living, He had created 'Rylan' and that was who he sends out to meet the fans or perform for the cameras, but he was really just a normal boy called Ross.

He had created a 'paper thin' identity. Poor Rylan/Ross knew this, admitting he'd never be happy because he must always craft this fake identity in order to earn a living. He is devoted to a lie.

In trying to understand our obsession with cheap celebrity culture Grayson asked us to imagine primitive man. In the old days, Ugg would be good at hunting, and Ogg would be good at thatching. Everyone in the village had a role for which they were known, or famous. Now we're just lost in a mass of people. In the rat race, working for the corporation and shopping at the impersonal chain stores our identity is diluted but by watching celebrities 'we get the feeling of being an individual, but on steroids!'

Kayleigh also rejected the identity modern culture might have foisted upon her: as a single mother of four, certain people might apportion her the identity of slut or scrounger.

She converted to Islam, obtaining a new identity overnight, one which was placid and quiet and content. She no longer wanted to wander around shopping centres, which was apparently what she did beforehand. Arguably, she didn't need religion, simply a hobby or a higher IQ. Nonetheless, as a Muslim she said she had stopped wanting to own 20 pairs of shoes. She was no longer 'buying her identity from the big brand shops'. Perhaps not, but she's simply in thrall to the mosque rather than the mall. Who's to say which is preferable?

This programme was brilliant viewing. It never allowed you to settle for one second. Just like the fluctuations in your identity there was a constant jabbing and twisting and jarring. One minute we're watching Grayson quietly sketch, the next he's smashing his artwork. We're watching dinner in Huhne's fancy kitchen then we're by a windy motorway in Kent. We talk of The X-Factor then Allah. How refreshing and vital it was. Nothing in the programme was constant.

Likewise, your identity isn't constant. The person you think you are is never set in stone. A million influences are impacting upon you and you just don't know it. You can't slip into your sensible suit and fasten your sensible shoes, and tuck the same newspaper under your arm and head off to catch the same train to the job you've had for 17 years and believe your identity isn't shifting. The world is working on you and you'd better get wise to it! After all, the one who claimed it isn't is the one who ended up in jail.