The pink lilies at Home Office reception are yesterday’s flowers and have wilted in the radiator heat. Like the lone receptionist blearily logging the early morning visitors, they look a bit limp.

The same cannot be said for the home secretary herself, who does not seem a bit jaded as she sweeps into the building. Jacqui Smith, the first home secretary in British history ever to have to worry about showing too much cleavage, is wearing a lacy black camisole under a scarlet jacket.

These days she is too wise to wear plunging tops at the dispatch box, but it’s clear that “Cleavage Day”, as she dubs it, did not put her off sexy outfits.

“Any woman MP knows what it’s like to have constant harping on about what you’re wearing,” she says levelly. “Cleavage Day was the Monday after I got the job. I was in parliament talking about the attacks on London and Glasgow that had happened the day after I got the job. How low cut my top was had not been top of my mind when I woke up in the morning . . .”

All the same, the excitement caused by her embonpoint was a rude awakening to the realities of life as a high-profile female politician. A few hours after our interview, Smith was accused of having a “love in” with Chris Huhne, the Liberal Democrat MP, after agreeing with a surprising number of his views on the BBC’s Question Time. “There will be times when you are treated differently as a woman. But it hasn’t stopped me doing what I do.”

If sexism was ever going to be a big problem for her, it would be now – as she faces down the police over pay. A recent study for her own department found that sexist language and behaviour are still “all but endemic” in the service. Officers are furious that she will not backdate a pay increase that is below inflation rates, making her an obvious target for chauvinistic attitudes.

Has she felt it? “I’m not so sure about the photo they’ve used of me on the Police Federation literature,” she says hesitantly. (The latest edition of the Police Federation magazine features an ugly mock-up of her as Jack the Ripper. “Jacq the rip off” has ruddy cheeks, a silly grin and a peroxide yellow wig.) “But apart from that, absolutely not.”

Smith is too smart to fall into the trap of bleating about her gender. That would just play into the hands of the officers threatening to march on Westminster this week. It’s a battle that Smith is determined to win.

“We were very clear that what happened to police pay had to be in line with what is happening to other public sector pay. Not because of any sort of mean-spiritedness, because actually in the end what impacts most on police officers and other members of the public will be what they are paying for their mortgages, what the inflation rate is and whether or not we can keep stability in the economy,” she says.

It is a row about £200 per officer – on the face of it, a trifling amount. But Smith insists that she is not into picking fights for the sake of it. Bob Marshall-Andrews, the veteran Labour MP, has described her as the “human and attractive face of the Home Office”.

“Just when I thought I’d arrived, he told me, ‘That’s in relation to your predecessor’,” she says. Her predecessor, John Reid, was notoriously pugilistic and no oil painting. Even her critics would agree that Smith’s style is very different from his.

“I’m pragmatic, but I know what’s at stake in this job, for the people who elected us as a government. Determination, willingness to work through the issues, trying to find the agreements and ways we’ll actually make a difference to people is very much my style.”

The big test of this approach will come when MPs vote on plans to extend the length of time that terror suspects can be detained without charge. Privately her heart must have plummeted when Downing Street bowed to pressure from police and security services to bring this old chestnut up again. The last attempt to extend so-called “detention without charge” led to a massively embarrassing defeat for Charles Clarke, the then home secretary.

Smith is determined it will not happen again. The proposals have been dramatically watered down and she believes they will be voted through. She explains the latest compromise she has made, but the words are unquotable – the kind of robot-speak perfected by Labour ministers who never deviate from the script.

She slips into the same Dalek-like language when she talks about what it is really like being home secretary: “It’s a massive honour, immensely interesting. It’s helping people to be and feel safer in our communities and within our borders. I really feel that this work is at the heart of what the PM wants to do to help people in this country get as far as they can on the basis of their talents, where everybody is able to get on with their lives and do the best they can . . .” And on and on.

It is hard to imagine this is anything like what she would say in private, about the endless fire-fighting, sleepless nights and 18-hour days involved in running a department dubbed by Reid as “not fit for purpose”. Her appointment was one of the big surprises of Gordon Brown’s first cabinet. Smith says she had no inkling that it was coming.

“The PM said, ‘I think you’re going to be shocked’, and I was. I’d [only] been a year in the cabinet.” Her old job of chief whip was relatively anonymous; the tricky business of cajoling backbenchers into supporting legislation they dislike is conducted behind closed doors.

A former economics teacher, she had been an MP only since 1997. Did she feel a bit green for a big job? “No. I feel, actually, there aren’t many people who have done as many different jobs as I’ve done, and been a minister as long as I’ve been, on either side of the Commons.”

On paper, or when she is on tricky ground, Smith is a great exponent of robot-speak – at times, reciting a telephone directory would feel exciting in comparison. It is a shame because, as a person, she is engaging, with a self-deprecating manner and ready laugh.

A cringeworthy photograph unearthed when she first got the job shows her in pyjamas playing a student drinking game called “bunnies” – suggesting that she does know how to let her hair down.

As an undergraduate at Hertford College, Oxford, she once went to a party wearing a black plastic bag. She has also admitted that she occasionally smoked cannabis. But she insists she was never a real party girl.

“No! There’s one picture of me taken doing some sort of drinking game. Have you seen any more of them? Do you know what – I’m the first woman home secretary. If there were any more photos of me in a wild party mode they’d be out there by now.” There’s no time for that kind of thing now – her job does not lend itself to much work-life balance, although she is still an Aston Villa season ticket holder.

She turns to the issue of violent crime, admitting that the government faces huge challenges to reassure the public that knife, drug and gun crime are not spiralling out of control.

“The truth is that people are safer, in terms of crime, than 10 years ago, but I do think we’ve got a big job to do to build people’s confidence. It’s also about the way people respond to the very small number of particularly violent incidents there are. Serious violence is something we need to address.”

Would she feel safe walking alone at night in, say, Hackney, east London? She looks alarmed: “No. Why would I do that?”

Perhaps deprived Hackney is an unfair example – what about well-heeled Kensington and Chelsea? “No. But I would never have done, at any point in my life. I just don’t think it’s a thing that people do. I wouldn’t walk around at midnight. I’m fortunate that I don’t have to do so.”

Later an aide calls me fretting about these comments. The home secretary might have given the wrong impression and meant no slight to Hackney. In fact the boss went and bought a kebab on the mean streets of Peckham, southeast London, after dark the other day. I somehow doubt she went alone; these days she goes nowhere without a phalanx of protection officers. No mugger risk there then.

Another high priority at the Home Office is binge drinking. Does she have any bright ideas?

“We’re thinking about how we get the messages out to young people: that you can have a good time without having a drink. There is more we can do with parents to help them to recognise the dangers of drinking. We’re already looking at the impact that both marketing and pricing are having.”

Would she consider drastic measures such as raising the legal drinking age? “I’m not convinced that raising the age is the right way at the moment. I’m much more interested in enforcing the current age. We are having success in doing that.”

Smith is popular among Labour backbenchers. “I like Jacqui. We all like Jacqui,” says one senior colleague, a little flatly.

Like but not admire, I suggest. “Like but not admire,” he agrees. Most politicians would prefer it the other way round. The odds may be stacked against her in this difficult job, but Smith still has time to prove she can be both.

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