The Camerons: Off duty but still firmly on message

David and Samantha Cameron today announced the birth of their fourth child, a girl. (BEN BIRCHALL - WPA POOL/GETTY IMAGES)

There's no such thing as a holiday when you're the Prime Minister. Nick Clegg may be manning the dispatch box in London, but Dave and Sam are very much on duty as they pose for pictures at Daymer Beach in Cornwall.

Ostensibly on a family holiday, they're also promoting Britain as the perfect spot for a summer break and themselves as just any other middle class staycationers.

In a way, Cameron has managed to pull it off. He has the look of an office worker on dress-down Friday, struggling to cope with the concept of smart-casual. Such a look is not an unusual sight in Cornwall, where bankers who don't know how to relax wield a bucket and spade in one hand and a Blackberry in the other.

Only someone deeply institutionalised wears smart loafers on a coastal path. That polo shirt, too, is rather dark and dour for a summer holiday; a bright Tory blue would have been a bit more jaunty. But it could have been a lot worse.

Sam Cam's studiedly sunny look is just as incongruous with the seaside surroundings as her husband's outfit; more suited to a Notting Hill garden party than the beach.

Then again, finding stylish clothes in the later stages of pregnancy isn't easy, and as usual she does look good. Maxi dresses are a spring/summer trend this year so she's firmly on message with this fluid empire line style.

While the couple's outfits may appear contrived, they haven't done badly, because the off-duty statesman look is notoriously hard to pull off.

Too casual – such as Tony Blair's infamous floral shorts which he debuted during a jaunt to the Caribbean – and you lack gravitas, which is fairly important when you're the most powerful man in Britain.

Too smart and you look inhumanly stiff, as Gordon Brown proved when he wore a jacket to the beach in Norfolk. But on balance, it's probably better to look as if you're running the country rather than a local surf shop.