New fashion 2013 end

That is not to say that Cressida doesn't scrub up nicely. A roster of summer society weddings showcased her weakness for boho maxi dresses in jazzy patterns paired with neat cropped jackets. For a pre-Wimbledon party (she's a keen tennis player) she donned a wafty jumpsuit, posing politely with her half-sister Isabella Branson. She's wisely steered clear of hats, leaving millinery statements to her friends the Princesses Eugenie and Beatrice, opting instead for hippie-ish flowers. Not for Cressie the thrice-weekly blow-dries; she prefers a more tousled, natural approach, and is as wedded to that aforementioned scrunchie as Kate is to her nude LK Bennett courts.

Cressie's way: boho chic at the wedding of Lady Natasha Rufus Isaacs; a maxi dress with a sequined jacket at the wedding of Lady Melissa Percy; a striking jumpsuit at the Ralph Lauren Wimbledon Party. Photo: REX, Getty

If Tatler' s October issue is to be believed, Bonas reserves most of her sartorially inclined energies for parties. Tatler tells us she is "obsessed with fancy dress" - and they've dug out all the old Bystander pictures to prove it, the highlight of which shows her dressed as a caterpillar as part of her 2010 London Marathon effort. But most encouragingly, the tabloids have yet to uncover a photograph of Cressie topless. That, as she herself might say, would be cringe de la cringe .