"Dave's down in London too and we try and spend as much time together as we possibly can," she says.

"Even if I've been working in the studio until midnight, I'll still go and stay at his, or he'll come to mine. Or, if I'm away and he's off, he'll try and fly out to see me wherever I am.

"And when we are together we don't do the whole party circuit thing. Because we are so busy, when we've got time off we just want to sit at home and watch a DVD or go out with friends for a quiet drink. It's just nice to get away from everything, to get all the make-up off and get my pyjamas on!"

It's hardly the sexy image that millions of male Sugababes fans have. But Heidi is adamant that, contrary to what they might think, the girls aren't deliberately playing up their raunchy side.

"I don't honestly think we've ever sold ourselves on that," she maintains, laughing at her own protest.

"Do people expect us to be sexy? I don't think so."

But there's no doubt that Heidi in particular is looking good for their comeback and she admits she's been working to get in shape.

"I've been with a trainer for the last few months because, apart from the fact that you know everyone's going to be looking at you on TV, you want to feel comfortable when you're on stage performing.

"So I've done it for myself as much as anything. I have lost quite a bit of weight, but it's only what I put on last year. I think it must have been too many takeaways at home with Dave!"