Why do military jets cost billions more than planned? Well, "it's a bit like buying a conservatory."

How many jobs are at risk at the MoD's centre at Abbey Wood, near Bristol?
"It could be as many as 2,000 jobs, yes. That is entirely within the realms of possibility."

Civil servants are normally cautious, tight-lipped people. Engineers, in my experience, rarely like sweeping statements. And military people are almost congenitally discreet.

So when I arrived to interview Britain's senior military engineering civil servant, I didn't expect much.

But Dr Andrew Tyler is renowned for his plain speaking approach. The man who leads 21,000 people who buy all the kit for the armed forces had clearly had enough of softly softly. He was fed up of reading stories about dodgy radios and unprotected land rovers; 'our brave soldiers let down by the pen-pushers', as the papers put it.

"It is one of my biggest frustrations that we are a bunch of bureaucratic pen-pushers," he told me. "Nothing could be further from the truth."

We walked around the calm landscaped grounds of the Ministry of Defence (MoD) headquarters near Bristol, and he pointed to an office block. "Every office here is in constant contact with the front line," he insisted. "The teams are just a phone call away from Libya, an email from Afghanistan."

Buying hi-tech equipment for the armed forces is not easy. Dr Tyler wants us all to understand how enormously complex it is. Having spent a day inside the nuclear submarine factory his team run, I can well believe it.

But does that excuse multi-billion pound cost over-runs?

The RAF's new fast jet, the Typhoon, is £3.5 bn over budget. It's worth spelling that out: £3,500,000,000 more than was originally estimated. How does that happen?

The standard tactic for disarming this dangerous question is to bore you to death. Defence officials bombard you with details of multiple tenders, of specification shifts, of sophisticated technology prototypes.

Andrew Tyler talks about conservatories. "You sit down with your wife," he tells me, as if we were leaning on the bar, "You budget for eight or nine thousand pounds, and as sure as eggs is eggs, when the builder leaves the premises you've got a bill for fifteen."

It's refreshing. The problem is in the initial estimates, he explains. 'Natural human optimism' produces low figures when the aircraft carrier or submarine is being planned. And then, just like the builder in your back garden, everything goes up.

He was just as frank on jobs. When the defence secretary announced, back in October, that a quarter of all MoD jobs would go by 2015, we all did the maths. 8,000 people work at Abbey Wood, so that sounded like 2,000 job losses. But for months, the MoD has been silent on the detail.

Not Dr Tyler. 2,000 job losses is "entirely within the realms of possibility". Abbey Wood is on a quest for even greater efficiency, he explains, and "that is definitely going to require doing the same thing with less people. It could be as many as 2,000 people, yes."

Now this isn't a bolt from the blue. He is essentially confirming what we already knew. People won't be leaving overnight, the process will take three years. A voluntary redundancy scheme is already proving popular.

But what is really remarkable here is the candour. We have grown used to Whitehall code, where everything is carefully couched and you have to read between the lines. Andrew Tyler clearly thinks that culture has brought us billion pound overspends and nervous staff. It is now time, he is saying, to be honest about what submarines and fast jets will actually cost, and tell staff how many jobs will actually go.

There is a footnote to this story. One of those jobs that will go is the Chief Operating Officer. Yes, Dr Tyler himself has been restructured out of the MoD. By the end of the year, his post will be no more, and he will be back in the private commercial world. Inside the world of defence contracting, people will remember him for lots of technical and substantial changes.

Outside, we will remember a military engineer who decided it was time to rename 'personal operational excavation devices', and call a spade a spade.

"I always say that any day when you don't see a submarine is a day wasted."

Jon Swift loves his subs, that much is clear. For an engineer, they are the ultimate challenge.

"We take a metal tube, put a nuclear reactor in it and a hundred sailors. Then we cram every available space with weapons and hi-tech equipment. Finally, we send it deep into the ocean. Everything has to be safe - and seen to be safe."

Mr Swift is also passionate about his job. Which is at once easy and impossible to describe. Simply put, he is in charge of making seven new nuclear submarines for the Royal Navy.

The actual metal-banging is done by BAE Systems (as well as a vast amount of computer-aided design and hi-tech system installation). 5,000 people work at the company's submarine yard in Barrow-in-Furness, Cumbria.

Royal Navy Engineers work alongside the civilians, ensuring everything is as they want it.

Jon Swift leads a team of 100 who do that very 21st century job: Project Management.

He is based at MoD Abbey Wood, a vast complex of offices perched on the ring road round Bristol's northern fringe. 8,000 people work here, civilians and uniformed people, finding, buying and maintaining every piece of kit used by the armed forces.

Abbey Wood takes a pounding in the media. When soldiers don't get the right kit in the desert, it's the 'pen-pushers of Abbey Wood' who are blamed.

Now Abbey Wood's top brass want to tell their side of the story. Two of us were invited in, to see the projects they are most proud of. First up, submarines.

In some ways it's a surprising story to pick, from an MoD point of view. HMS Astute, the first of the new breed, already has its own archive of news stories. First, there was the unfortunate episode off Skye, when she ran aground in sea trials. Then there was the tragedy in Southampton Docks, when a crewman turned a weapon on an officer.

"Abbey Wood is the office," he smiles, "but here's where I come for a dose of engineering. Being part of the submarine programme gives you great pride: the power, the stealth, the sheer complexity."

I have never been in a factory like this.
And with good reason. There is no other factory like this.
No-one else makes nuclear submarines. And that can be a problem.

If Jon Swift and his team don't like what BAE Systems are doing, they can't go anywhere else for their subs. BAE Systems have a monopoly. Of course, he points out, this is also a "monopsony" (now there's a word for scrabble lovers). Jon, and the Royal Navy, is the only customer. Who else buys nuclear submarines?

"It's like a marriage," he explains, "but not one that's going to end in divorce. We work very closely together. I have a team of 30 people here on site, it's all very hands on, eyes on." Unlike a normal business relationship, both sides see each other's numbers. Both sides need this programme to work. And yes, there are low points as well as high points.

Probably the lowest was the day the National Audit Office published the increase in costs. The MoD's original estimate for the first three boats was £2.58bn, but they have come in at £3.8bn, a cool £1,200,000,000 over budget. And that is definitely one of Jon Swift's jobs.

"It's absolutely important that we deliver on time and to cost, but the difficulty with these complex major projects is getting those original estimates right."

It is true that few experts question the final bill. Around a billion pounds for a nuclear sub is "the going rate", one told me. The problem is those early estimates, when ministers want to hear good news, and everyone involved guesses low. Then things get complicated. Jon Swift's team check every increase, but gradually the bill heads north until we have a billion pound overspend.

We stand high in the dockyard now, on a gantry above both submarines. John Swift looks down on them, with affection as well as pride. It is his job to defend the public finances of this project, but also, I realise, to appreciate the engineering.

"The astute class submarine," he smiles, "she's big she's black and she's awesome, and like any primadonna, she's worth waiting for."

In July 2011 the last Hercules will leave the RAF's base at Lyneham, in North Wiltshire, for ever. The base has been home to the cargo fleet for decades, but the MoD only wants one long haul airbase, and that is to be Brize Norton, just up the road in Oxfordshire.

The burning question, then, is what happens to the Lyneham site. It is vast, 1,300 acres. It brings in £90m to the pubs, taxis and traders of North Wiltshire. Close on 3,000 jobs depend on the base indirectly, according to the local chamber of commerce.

Eddy Shah has a plan. It's ambitious, in fact it's pretty spectacular. It features a snowdome; a Wiltshire Theme Park, complete with replica Stonehenge; an education centre and a thousand eco-homes.

"Heston Blumenthal is signed up to the catering plan," explains Eddy, as he likes to be known. "We've got over 1,000 acres here, we've got a bit of everything, I think this is a new kind of industrial revolution."

If you want to see the plans for yourself, have a look here.
LynehamPropoalsEddyShah.pdf

Now Eddy Shah is a strong salesman, and he makes his case spectacularly. He takes me to an abandoned naval training station near Corsham. HMS Arthur once trained a young Prince Philip, but twenty years ago it was closed, and nothing was done with the site. The place is now crawling with brambles, and covered in graffiti.

"My fear is that this is what will happen to Lyneham," he tells me. "If the MoD don't get a move on and make a decision, it will just go to wrack and ruin."

It's a strong campaigning tactic, for sure. But is it a little, well, hasty?

There is evidence the MoD is looking hard at a military future for the base. 20,000 soldiers and airforce personnel are on their way back from Germany, now the Cold War is well and truly over. Homes and training bases must be found.

"The Army want to come to Lyneham," the local MP tells me. James Gray has been lobbying hard, and is on good terms with both Liam Fox, the Defence Secretary, and David Cameron. "They've both told me Lyneham has a very good case," he insists.

In fact, just last week I happened to hear Liam Fox at a Chamber of Commerce dinner in Bristol. He was making a speech, he could pick his subjects. And he chose Lyneham, interestingly. Taxpayers, he told us, are paying £250m a year to keep troops in Germany - and that is just on allowances.

"I would much rather spend that money in the British economy," he said, to much applause. My ears pricked up, because Liam Fox could have kept quiet. He was in Bristol, after all, and talking to a business audience. Why mention Lyneham, unless you are minded to send some work its way?

I put it to Eddy Shah that perhaps he was telling people the MoD would abandon Lyneham simply to bolster support for his own, commercial, plan. He laughed that one off. "I'm 67, the last thing I want is another big project! No, the message is clear - MoD: make your mind up. Otherwise, this community will die."

The Ministry remains tight-lipped. A decision will be taken before the Parliamentary break in the summer, I'm told. Well, if they decide to close Lyneham for good, Wiltshire may soon have a new theme park for skiing druids.