How often do you call your mother?

The phone call home to mother is an institution of family life. And like many institutions, it operates according to arcane rules. Every family has them. But every family's are different.

Ever since I left home, 20 years ago, I have called on a Sunday between 5pm and 6pm. At first this meant taking a £1 coin to the payphones at university: the length of call was always predetermined by the same denomination. At that hour, there was always a queue, and everyone on the phones was calling home, while everyone in the queue listened (only one of the three booths was enclosed).

However, according to research carried out by OnePoll for the telecommunications company TalkTalk, the most common time to call home is Monday at 7pm – after work and before the decent telly starts. The average length of call is 22 minutes, while I think I usually clock up 40. (Mum thinks it's 20, but the call log begs to differ.)

Is this tradition motivated by duty or need or consideration or pure pleasure? One colleague I speak to has just come off the phone to her mother at 10am. "She calls me every day," she says. "I don't always pick up." Another calls home once a fortnight. A third never calls, but only receives. More witnesses are needed.

Two women are walking towards King's Cross station. Amanda Raphael is pulling her mother's suitcase. She says they talk "three or four times a week. Mum's on her own. It gives me peace of mind." "And if I've got a problem, I call her," says her mother, Janet.

This is slightly shaming. But my mother is not alone. Alan, 55, a construction worker from Oxford, visits his mother every week. "And she phones. She says: 'Are you OK?' but really what she wants is for me to see if she is OK." That seems harsh, but then he does visit often.

Scarlett Saunders, 19, laughs at the question. "I never call my mother. She calls me. Is that really bad? I'm usually in a bit too much of a rush. But I do call her if I'm upset or ill."

Time to pick up the phone. A pity it is for work reasons. Hi Mum, it's me, even though it's not a Sunday. Why is it so important that us kids call home every week?

"Mothers worry whether their children are all right. And, second, they look forward to a chat." Then she says: "I do know of some children who speak to their mothers every day." Crikey. This is not going well. "But I think that's probably a bit much."

So, are we roughly all OK in the phone-call department?

"You're very good," she says, kindly. Which is all I really needed to hear.