'I always write songs about my life,’ says Taylor Swift. 'And if you’re horrible to me I’m going to write a song about you and you are not going to like it. That’s how I operate.’

Sweet, perfect, teetotal, Pollyanna – these are the words most commonly used to describe Taylor Swift. Which is odd given that she makes no attempt to conceal her less angelic side.

We’re talking about Better Than Revenge, a song in which she describes a love rival as 'an actress/ but she’s better known for the things she does on the mattress’.

It’s assumed to be about Camilla Belle, who was linked with the Disney star Joe Jonas mere days after he dumped Swift in a 27-second phone call. But of course she will neither confirm nor deny this.

'I’m the only person who knows who [my songs] really are about and there’s comfort in that,’ she says with a hint of a smile.

Taylor Swift, with her apple-pie image and candid chronicling of her love life, has hit upon a winning combination.

The 21-year-old’s latest album, 'Speak Now’, came out last October and sold more than a million copies in its first week of release. That’s more than any other album in the past 15 years.

Last year she won four Grammy Awards and broke Beyoncé’s record for the most top-40 singles by a female artist in the past decade.

Her previous album, 'Fearless’, was America’s biggest-selling album of 2009 and she was America’s overall biggest-selling artist of 2008.

She has conquered her homeland to the point where the Wall Street Journal, not a paper given to celebrity coverage, ran a feature just before Christmas complaining of her ubiquity.

So now she’s in London seeing off the final week of her first world tour. She’s been through Germany (which 'really reminded me of where I grew up in Pennsylvania. We lived in a really old farmhouse with 10 acres and grew Christmas trees and had lots of animals’) and she’s just been in Madrid.

'We were doing a show at the weekend,’ she says. 'And I could count at least 10 people who were crying.’ World domination may not be hers yet but it’s clearly not far away.

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