There were some frank scenes, though. I was still kissing a lot of men a lot of the time. Then I had to go home to my husband and it was strange sometimes. I had to do it though, it was in my contract. I was forced to kiss all of those men! Matthew was okay about it though. There hasn't been any post-traumatic stress - yet.

When was the last time you were drunk?
i don't actually drink at all. I'm not an alcoholic or anything, I just don't like the taste of it. I have no problem with people enjoying a drink at all, but I don't find it relaxing. Strangers buy me Cosmopolitans when they see me out thinking I am like Carrie. I just have to pretend to take a sip and then give it to a friend.

So when your character dances, when drunk, in The Family Stone, you didn't know how she felt?
I had no idea. In fact, that particular scene was the hardest I've ever done. I don't dance in real life. I don't go to clubs or dance at parties. I am happy that everyone else does and I love watching. So that piece of acting was really embarrassing.

Do you have any bad habits?
I live a very clean lifestyle actually, I have never done more than smoke a cigarette in my life. The first time I saw someone take drugs was a couple of years ago. I was stunned. I was at a party and had walked into a bathroom by mistake. The moment I saw what was happening I turned on my heel and went. I was quite scared actually, I left very quickly. I was convinced there would be a police raid or something. I felt as though I was in the film Scarface and I didn't like it. I know nothing about that sort of thing, it is just not a circle I travel in.

You celebrated your 40th birthday this year. Did it change you at all?
I was on set of The Family Stone on my birthday. It was a bit of a strange day for me. I remember at one point looking over at Clare Danes and thinking:'Oh my god, you are only 26!' That is when I realised I was 40. Apart from little things like that it hasn't really made any difference to me or my career.

How is motherhood suiting you?
Becoming a mother is a complete life change. You suddenly have to think about someone else all the time - and that can be tough for an actress. My little boy who relies on me for everything and it is such a responsibility. But I love my life. I love having having this little boy to answer to and a husband to care about. It is a wonderful life which I wouldn't ever want to change.