It's been a fairly gloomy start to the summer so far in the UK (although, ever-optimistic I'm banking on a promised a heatwave any minute now), but nothing's going to stop Mumsnet users planning their holidays, home or abroad.

Alongside the obvious vacation conversation topics – destination, mode of travel – there's a hardy perennial that women tend to discuss only among themselves: what sort of swimwear can I get away with by the pool this year?

Of course, the sensible position (aside from "flat out on the sand with a book") is to wear whatever you darned well please, so long as you're not breaking any by-laws or being actively frightening.

This is, generally, the approach taken by men and children: it's hot; I will wear a swimming costume; where's my inflatable ring with integral drinks holder. End of dilemma.

As the recent outrage over a protein company's "beach body ready" advertisement showed, lots of women are getting increasingly irritated at the assumption that they should give their swimming gear any more thought than that.

"Am I beach body ready? Yes, because I have a body and I can get to the beach," they cried. They are – of course – entirely right. But that isn't going to stop women who've borne a child gathering together to metaphorically assess each other's stretch marks and stroke their chins in the manner of a garage mechanic who's been asked for a quote.

Bikinis at the ready?

"When do you become too old to wear a bikini?" Mumsnet users enquired. ("When you're dead," came one unimprovable reply.) Many stoutly defended the right of any woman of any age to wear any two-piece that takes her fancy – "I didn't even start wearing bikinis until I was in my forties" said one, fearlessly – but lots of contributors admitted to tenacious personal hang-ups. "I need something to hold my tummy in," wailed one poor soul, speaking (frankly) for lots of us, and not just when we're on holiday either.

Those who proudly came out as long-term bikini wearers tended to fall into one of three categories: the long-bodied like myself (for whom one-pieces mean an endless picking of swimsuit bottoms out of unmentionables while simultaneously worrying about inadvertent toplessness); the lovely of abdomen (those who have toned muscles through hard work and good food choices, and those who have avoided stretch marks through sheer dumb luck); and those who simply have enough self-confidence to wear whatever pleases them.

"I have a straight up-and-down body," says one; "I look like a breezeblock in a one-piece." Another, in a bracingly realistic mood, noted that whatever you're wearing, "there's always going to be someone there who looks a lot worse than you"; not the kindest thought, but guiltily consoling nonetheless.

So what do we wear at the beach?

Thankfully, you can always turn to Mumsnetters for practical tips. Go for 1950s-style retro high-waisted styles if you like a bit more structure around your bottom and midriff.

If you're substantial of chest, look for brands that offer proper bra-like support; consider leaving the spaghetti straps and itsy-witsy cups to those less rich in decades and experience, and seek out some proper scaffolding. And if anyone is rude enough to question your choice, you can always tell them your doctor has told you to get more vitamin D.

As often happens on Mumsnet, a simple conversation about an "everyday" issue reveals a lot about how folks think about themselves and the world. Mumsnetters – indeed, mothers on the whole, in our experience – are a clever, independent-minded bunch; but when it comes to exposing our midriffs and buttocks to a crowd of strangers, it can be incredibly difficult to throw off a lifetime of conditioning telling you that only slim, young and lovely will do.

On one point, though, we are pretty much unanimous: there is absolutely no "rule" about the age at which anyone should stop (or start) wearing anything. Although, if you were to really press me, I might make an exception for corduroy dungarees, which really are best left to the under-fives.

Justine Roberts is founder and chief executive of Mumsnet and Gransnet. She has also sat on the Expert Steering Group on Family Support Services, the Consultative Council of the British Board of Film Classification and the Commission on Civil Society and Democratic Engagement.

You can find her own Twitter @Justine_Roberts, or visit the Mumsnet page @MumsnetTowers. Alternatively, for all information about Mumsnet please visit the website here.