The Ministry of Defence is a frantic place. We are marched into a waiting room. As we linger, the door is flung open, and a bearded figure with a nautical air, bearing a faint resemblance to Lord Alloa in the 39 Steps, gazes in and clocks us. "No," he barks, and slams the door shut. It opens again, and we are rescued by Hayden Allen, Liam Fox's toiling Special Adviser. As he walks us out towards the Defence Secretary's Office, we half-wonder whether the right course is to salute any passing staff, or whether they are mistakenly about to salute us.

Fox, too, is pressed for time. Prime Minister's Questions will begin in forty-five minutes flat, and he has a meeting to squeeze in between now and then. We will therefore cram in as much as we can. And there is as much to ask the Defence Secretary as any other Cabinet Minister, perhaps more. In little over a year, his tenure has seen the first strategic defence review since 1997, the start of a spending scaleback unprecedented in modern times, a new military front open up in Libya, and David Cameron's announcement that our combat troops will leave Afghanistan by the end of 2015.

And the Defence Secretary is a compelling figure in any event: former leadership contender, leading man on the party's right - perhaps the leading man - and Minister whose personal relationship with Downing Street is repeatedly reported to be tense and whose confidential correspondence has twice been leaked. We admit that we'll open with a left-field question, and Fox's eyes dart upwards in wary anticipation. With the News of The World hacking scandal sure to be raised at PMQS, has he ever believed that his voicemail has been broken into? "Have I?" he says, perhaps considering the question for the first time. "No." That settled, we move on. First things first: is the MOD fit for purpose? Fox says that "we inherited what was a historic mess, and the challenge was enormous". He goes on to argue that Labour had "never really taken an interest in the MoD as a department or as a business, but if we were in the private sector we would be the third biggest business in the FTSE". Consequently, he believed in opposition that "if you go for sequential reform and you’ll not get reform, and you have to really unleash the whole process, understanding that would be stretching for all of us, the politicians and those who work here".

Swiftly and fluently, he reels off his planned reforms. A new major projects board. Regular reports made to it by management teams. "Remedial challenges" if they don't succeed in meeting targets - "and if they fail to meet them at the next quarter we’ll publish to the stock market the element of the contract we feel to be at risk"". There will be a new joint force command, a "fourth pillar in defence", to deal with cyberspace and electronic threats. He wants this pillar to be free of "the stove piping in the traditions of the three services" which can mean that "if you don’t come from the right part of the right service that you’ll never get to the top".

The other big reform, the Defence Secretary says, is "the devolution of budgets back to the armed forces". He wants senior officers to take more responsibility - and with it, clearly, praise or blame for the decisions they make. "Up till now ministers have had all the control and so you’ve had civil servants and service chiefs who have felt disempowered in the process.Well, I’m giving them that responsibility back, but believe me I’m going to hold them account for it. You might get me now briefing in the press against the armed forces, if they’re unable to deliver what the government wants."

Fox seems to feel that he may have been risking his arm with that jocular last sentence, adding that "the correct process, seriously, is that the government should determine the outcomes and the outputs that we want the armed forces to have and set the budget within which they must provide it". In his neat way, he produces a formula for reconciling the apparently irreconcilable aims of a bigger defence bang with a smaller financial buck: "although people say it is difficult being both a hawk on the budget and a hawk on defence, ultimately they end up in the same place because if you’re not one you cannot be the other."

He insists that the right strategic choices have been made. "People say, well, if you’d had Harrier you’d have been able to use them in Libya. Actually, the choice of aircraft was dependent upon the choice of the weapons we used, and we chose to use high-end weapons, low collateral-damage weapons, Brimstone and Storm Shadow, which Harrier couldn’t carry. It needed bigger, heavier aircraft and that’s why we used Tornado. So even if we’d kept Ark Royal, and even if we’d kept Harrier, we would still have used Tornado from a land-base in Italy to carry out the mission in Libya."

And he makes no bid to re-open the financial settlement on which the defence review was founded. "It’s no secret that the initial plans were to see a much bigger defence budgetary reduction than we ended up with, but then that’s what we’re for, we’re Cabinet ministers and we fight for our departmental interests - and I did, and I think we got a reasonable settlement." He dismisses claims that the costs of the Libyan expedition could reach £1 billion by the autumn, projecting from costs so far a sum nearer £250 million: "I don’t have any reason to believe that we’ll need to revise that estimate."

On Afghanistan, is the Defence Secretary confident that after the withdrawal of troops there won't be a bloodbath and an Islamist state? He replies that "I think at the current rate of progress there are sufficient grounds to believe that the Afghan security forces, while not perfect, will be good enough for the task." We point out that this is not exactly a vote of confidence. "Well, as I say to people who tell me they can predict the future: how often have you won the lottery? We need to assess it as it goes on.” The delivery of basic benefits to Afghans - dispute resolution, the delivery of basic social services - "will be crucial".

He has said that Iran could have a working nuclear weapon by next year. Does he still take that view? Fox, a hawk on the subject, was reported to have been ticked off by the Foreign Office for making the claim, and he doesn't repeat it to us. "We are constantly assessing, of course, what we believe from intelligence to be the state of Iranian capability. They are progressing and, in my mind, they have absolute intent to get to a weaponisation programme…We have to make it very clear to Iran that them becoming a nuclear weapons state is not acceptable."

Fox is now on time, not to mention message, and is due that afternoon to have his first conversation with Leon Panetta, America's new Defence Secretary, a week or so after his appointment. As we leave, he insists that entering the Coalition was the right course to take, since it provides a platform for deficit reduction and welfare reform. And he flashes out at the end that he remains "an unreconstructed Atlanticist and Eurosceptic", though when asked what he'd like to see in the next manifesto he soon steers the conversation dexterously back to his responsibilities. 

None the less, his opening words of answer to the last question linger. "My first thing is that it should be a soundly intellectually-based agenda which should be about the empowerment of the individual citizen within a secure state that will protect its citizens from internal and external threat." Soundly intelletually-based. Is that a hint that too much policy has been shaped by polls, fashion, the needs of the moment? Whether so or not, this is a man with heavy responsibilities. Though he says that he's now writing fewer of them, he notes that "one of the saddest jobs I have is writing condolence letters to the families of those who’ve been killed."