Looking for a nice frock for today's photo shoot, Lily Allen walked into one shop in Ladbroke Grove and saw the assistant virtually dive across the room in an attempt to stop the Amy Winehouse CD playing in the background. She arrives back at the shoot and immediately starts discussing the possibility of gastric bypass surgery due to being "fat", then announces that it is all "off the record", even though she will post the whole thing on her MySpace blog within 48 hours. Mark Ronson, enjoying unexpectedly huge success with his Version album, seems less besieged by life, chatting happily about Prince parties and meeting Mani. She is the sort-of demure English rose. He is the smart-talking New Yorker. They are Dempsey and Makepeace of pop and today, On the eve of this weekend's Glastonbury festival Lily Allen and Mark Ronson seem like the best of friends ...

To kick things off, please introduce each other to the Guide.

Lily: This is Mark Ronson and he is an overrated, over-hyped pop producer from New York City. He's basically a DJ.

Mark: I think Lily Allen is one of the most gifted pop melody writers of her generation.

Lily: ONE OF? Who are the others? (Guffaws)

Mark: Anyway, Lily and I are friends even though I've never done anything nice for her.

When and where did you first meet?

Lily: It was at [Notting Hill club night] YoYo.

Mark: Yes, you put that smiley face pin badge on my really expensive leather jacket. I was almost crying.

Lily: I told Mark I was a singer and he went, "Oh, give me a CD then".

What was on the CD?

Lily: Smile, and a couple of demos from when I was signed to Warners.

Mark: I actually had to ask you twice for the CD.

Lily: Oh come on - you were not interested at ALL!

Mark: But then I listened to it on the plane, and ...

Lily: No you didn't! You listened to it about six months later!

Mark: BUT I WAS ON A PLANE. So anyway, I asked Lily if I could play it on my radio show, and then I asked her to come out to my studio [in New York] and sing Oh My God for my album.

Lily: NO! You asked me to suggest some songs for your album, then you gave all the good ones to other people! Then you went, "Oh, you can have the Kaiser Chiefs". THANKS! And then I said, "Oh, can you do some stuff for my album?". And you said, "Yeah, for $200,000". Hahahaha!

Busta Rhymes is on the new version of Oh My God. Was he expensive?

Mark: Well, as soon as I knew it'd be a single I called him up ... I thought he might not get it, but he understood it immediately. He gets about $60,000 every time he rhymes on a record!

Lily: $60,000 isn't much.

Mark: It's kind of a lot, Lily.

How much did you pay him?

Mark: Erm, something in the neighbourhood of a nice car.

Lily: Bentley or Golf?

Mark: Let's say a second hand Bentley. He got arrested half an hour after he left the studio ... (Distracted by mark on Lily's arm) Are you self-harming? What's this?

Lily: Yeah, I'm self-harming - I just want to be Amy Winehouse.

Mark: AHEM! You see THAT'S why you walk into a shop and the people behind the counter turn Amy's music off! You've got beef Tourette's!

Who's the worst drunk?

Lily: Me.

Mark: Yes.

Lily: I get really aggressive when I'm drunk. None of my label bosses will take me out any more because after one glass of champagne I'm standing up going "And another fucking thing! People like you are ruining music! You're ruining our country! Let me do it and I'll fix it!"

Would either of you say that you had normal childhoods?

Mark: I'll never say I had a normal childhood. My dad would manage bands - I'd come down in the middle of the night and Keith Moon was there playing air drums. That's not a normal childhood.

Lily: For the first 11 or so years of my life things were, well, not so nice, and we lived on a council estate. The thing is, I'm proud of being middle class now - my mum was working class, as was my dad, and they worked really fucking hard to provide me with what I had. Well, my mum did. It's funny when Lady Sovereign said that thing about me, "She doesn't have to work as hard as me because her dad's Keith Allen". Do you know what, Lady Sovereign? HAVE my dad. Go on! I'd love to see how many people buy your records. Go on! Take him!

Having said that, your first deal did come about because of your dad ...

Lily: Yeah, and it didn't work. It was rubbish folk music - my dad and another guy wrote it all. Then it didn't happen. Things only worked for me when I worked really, really hard myself.

Well done, Lily. Do you think the two of you would ever have met without having come from privileged backgrounds?

Lily: Probably not. You bump into people in LA, and they go "Oh, it's such a small world" and really it's not - it's just that you all go to the same places where you spend pounds 7 on a drink. We're bumping into each other in the middle of Ghana.

Mark: At the same time the reason we met is that I was DJing at YoYo. And so we could easily have met anyway. While I shouldn't care those exaggerated myths do just make me cringe. It's all stuff like "You hung out with Stella McCartney and had picnics with Michael Jackson".

Did you have picnics with Michael Jackson?

Mark: No. I did have a sleepover once ...

Lily: WHAT?

Mark: Er, yeah, I did. It was at Sean Lennon's house ... And ...

Lily: YOU DIDN'T! Did he do anything to you?

Mark: Oh, this is just going to get ridiculous. Thing is, Sean was friends with Michael Jackson when he was growing up and when we were about 12 years old he was like, "Michael Jackson's coming over tonight". I remember turning on Channel J which is the public access channel and ...

Lily: ... and Michael Jackson unzipped your trousers and ...

Mark: No, and so Channel J had this picture of this girl with her top off and Michael went (handbag action) "OOOH! Turn it OFF!" And me and Sean were like, "Why? This is great!".

What time did you go to bed?

Mark: We went to bed at one o'clock and we closed the window because there was a draught and he didn't want it to interfere with his voice. He slept on the floor.

Lily: FUCKING HELL. (Clapping like an excited seal) Ronson! I can't believe you slept with Michael Jackson!

Mark: Nothing happened!

Mark, is Stop Me still attracting hate mail from Smiths fans?

Mark: Not recently. I got two things from this little 15-year-old boy, going, "I want to stab you in the eye ..."

Lily: He phoned me up asking about what to do! I get things like "Give me a grand and I won't slit your mum's throat". So cheers for that. I've got five mobile phones because of all the hate phone calls. "I'm going to kidnap your dog." Please.

What don't you like about each other?

Mark: Lily's one of the few people I'm naturally intimidated by.

Lily: Why?

Mark: Not in a bad way ... But you're a bit "cult of personality" ...

Lily: No I'm not! People say I'm a complete bitch and I'm not, I'm just really insecure and when people meet me I'm just ... not very good at it. But I'm a nice person. I bought Mark a kebab only today.

What has Mark done for you, Lily?

Lily: He definitely needs to do more. It was my birthday the other week and I still don't have a present from him. One time I was on the fire escape of Mark's studio in New York, crying because I'd split up with my boyfriend. He came out, saw me crying, and went back inside! Hahahaha!

Mark: I'm not Joan Collins!

Lily: What?

Mark: Hang on. I'm still trying to think of something nice I've done for you. There must be something.

Lily: Mark, there's nothing.

· Lily and Mark play Glastonbury this weekend. Oh My God is out July 16. The Guardian sponsors Glastonbury