Get a bit of nerve and tell them that its illegal to ask that question then. If the answer will get you out of a job then maybe standing up for yourself might impress them? I've certainly told an interviewer that in the past and still got a job.
i have recently completed a degree and i am entering the world of work. my main problem is at every interview i am asked if i have children and technically you can't lie about it but it is illegal to ask this question!! It is indirect discrimination (can be classified as direct) and why if i have a child in the 21st century am i expected to stay at home with her for holidays and if she is ill.