The most impressive mother I know, the one who always has time to build scale models of the pyramids of Giza out of match-sticks, who knows the names and star signs of the Jonas Brothers, who never insists on public kisses outside the school gates, is partial to the odd cigarette. Not a full 20-a-day habit, mind you, but the odd gasper between school runs.

Although this is the woman most likely to make your children sigh and wish you could be more like her, her one small vice would make her ineligible to foster children for Redbridge council. And that means any children, even those old enough to have their own serious bike-shed habit.

Foster parents can be single or married, gay or straight; they can even, in some boroughs, have a criminal record (as long as it doesn’t involve violence against children). But these days, if they want to foster children under the age of five, they have to give up the fags. Redbridge’s decision to extend the absolute ban on smoking for foster parents of children under five to those with children of any age – despite a shortage in London alone of about 2,000 foster places – is one of those decisions that make most parents shiver as they pour their second glass of chardonnay.

Sometimes, in the dark passages of the night, I wonder whom I would leave my children with if my husband and I were wiped out by a Portuguese lorry driver. When I review my friends and relations for their suitability, I tend to dwell on their sense of humour or lack thereof, their Uno skills or their ability to help with maths homework while cooking fish fingers – oh, and their ability to hug little children however snotty or smeary.

I wonder if my children’s guardians would read bedtime stories until their jaws ached or spend three hours a week combing for nits, not to mention willingly enter the seventh circle of parental hell that is Claire’s Accessories.

The factor that doesn’t enter my small-hours calculations is whether any of these putative guardians smoke. I don’t smoke and I am not particularly fond of it as a habit, but if I had to choose someone to look after my kids it would be the state of their hearts, not their lungs, that would be the clincher.

That view puts me directly at odds with the prevailing wisdom, as expressed by experts such as Professor Robert West, director of tobacco studies at Cancer Research UK, who says: “Smoking around children can exacerbate asthma, increase childhood cancers and make them more susceptible to respiratory problems. Fostering is a difficult area and, although it sounds harsh, I think this ban is a good thing. On balance, you have to go with the health of the child.”

If that’s the case, it is just a matter of time before the only candidates eligible to become foster parents are those paragons who do not smoke, drink or eat chips or chocolate – and who exercise five times a week to 70% of their maximum heart rate. In other words, Olympic athletes in training (provided their drug tests are up to date) and Madonna.

In an ideal world, no foster parent, or birth parent for that matter, would smoke, drink, overeat or slump in front of the TV eating takeaway pizza; but in an ideal world no children would find themselves in circumstances so desperate that they would be taken into care. In an ideal world we would not have the highest teenage pregnancy rate in Europe, nor the highest divorce rate, nor the most single parents. I wonder how many prospective birth parents in this country would pass even the kind of vet-ting that Battersea dogs’ home undertakes to make sure its pets receive what they need to feel secure: a daily routine and love.

Given that, after adoption, long-term foster care is the best solution for children who have fallen victim to our less-than-ideal parenting skills, the ideal world is probably the wrong place to begin. “It’s crazy to have rigid criteria for foster parents,” one long-standing member of an inner-London adoption panel said. “Young, inexperienced social workers should not be allowed to rule out potentially loving foster parents because they have a bee in their bonnet about smoking. What we need is more common sense and fewer questionnaires.”

Quite a few readers will have grown up, as I did, with a parent who smoked, and those of us who haven’t yet perished from passive smoking would not swap our childhoods in the shadow of the ashtray for the most smoke-free of children’s homes. I suppose if you are a young social worker trying to determine whether people are “suitable” to foster, it is at least possible to tick with some certainty the “nonsmoker” box, whereas there is no saliva test to determine which would-be parents have the patience to sit through High School Musical 17 times.

I suspect that behind local-authority rigidity over smoking is the worry not that a child will grow up with asthma, but that the child will one day meet a lawyer who sees the opportunity to sue a public body for negligence. What a miserable comment on the way we live now, I don’t know which survey results I found less surprising this week: the revelation that men prefer blondes but marry brunettes or the discovery that 62% of fathers polled enjoy going to work because it gives them a break from their children, 40% of fathers find it really stressful to come straight home from work to a houseful of rowdy offspring and a quarter of dads admit leaving home early and coming home late so they can spend less time with their kids.

No mother who gets the six o’clock “something’s come up” call is going to raise an unplucked eyebrow at that one.

More interesting would be a poll of working mothers: how many find their offices a place of sanctuary, or dread walking through the door at 6pm because they will instantly have to become a cross between Florence Nightingale and Ban Ki-moon? My guess is that women would freely say they work for the money or for their children’s future, but because every working mother feels guilty somewhere in her core, she will never admit that she goes out to work because it is . . . easier. We leave that line to the men.

Rachel Johnson is away

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