Harriet Walker: No wonder we're taking off our clothes

There was something wrong with the picture of an ageing actor with a giggling starlet on his arm splashed across some of yesterday's papers. And for once, it wasn't because they're getting married, having a baby or engaged in any other self-delusional pursuit of eternal youth or delayed decrepitude. It's because they look like they're attending events in two different hemispheres – even though they were actually sharing the same red carpet in sub-zero London on Tuesday night.

Harrison Ford, 68, is cosily wrapped up in a wool suit with a spiffy spearmint-coloured scarf, while his co-star, Rachel McAdams, 32, turned up in a cutaway sundress, slashed to the navel and hanging from her skinny shoulders by suspender straps, her xylophonic ribs exposed to the elements on either side. (The wind force was at 5 on the Beaufort scale, I'll add.)

Now, I like going out without a coat as much as the next girl who's unwilling to compromise an outfit or pay a cloakroom charge; I am not one to lecture others on the virtues of dressing for the weather. But when the comparison is quite so stark – namely that Harrison dressed for heat and Rachel for Honolulu – it does make me, and probably plenty of other chilly people, wince. And it's a practice that gives women a bad name. Ford may well look smug in his woollens – better that than looking like he woke up from hibernation three months early.

Coming hot on the (extra-high, potentially incapacitating, no doubt) heels of Miriam O'Reilly's Countryfile case against the BBC, McAdams' frostbite fashion is further proof of the scrutiny and pressures that women in the public eye are subjected to. Expectations are heaped on them to be perennially glamorous, thin and young, regardless of temperature or time elapsed since their 21st birthday. This is nothing new, of course, but these two cases throw our attitudes into fairly harsh relief.

That the standard response to dealing with wrinkles in the age of high-definition TV should be "time for Botox", and that the only sartorial choice for a high-glamour event during the coldest winter on record should be – but of course! – a dress more suited to a beach wedding, is surely evidence enough that we've all gone a little bit mad.

It's natural, understandable, even reasonable to want to look good for the camera, whether it's publicity paps at a premiere or a satellite precision zoom-lens in your grill as you ride on the back of a tractor. Don't scorn women for dressing up a bit or wearing the sort of fantasy frock that you wouldn't be able to run for the bus in; I'm not saying Rachel McAdams should have worn a parka and boots. But don't let things escalate until celebrities and civilians alike look like fashion-obsessed fools, vanity-ridden desperadoes or meteorological ingénues so eager to show a bit of skin that we end up wearing bikinis in the snow. Obsessing over appearance is, ironically, never an attractive quality and it makes idiotsof us all.

Harrison Ford – he who wore the sensible scarf – has complained meanwhile that there are no roles for ageing actors in Hollywood any more. "Much as I understand the notion that there are no good parts for older women," he told reporters, "I want to make it abundantly clear that there are no good parts for old men either." He doesn't seem to do too badly (although we haven't seen Morning Glory yet, of course) but it's almost a relief to hear someone voicing the case for non-gender bias. Our obsession with good looks, full heads of hair and plumped, sag-free skin will lead to a preternaturally bland set of screen idols. It'll be the most contrived piece of theatre since women were played by young boys.

Coming to a screen near you: Waiting for Godot featuring Matt Damon and Ben Affleck! King Lear played by Justin Bieber! And he'll be wearing Bermuda shorts for the storm scene.