Des Browne, the secretary of state for defence and likely to be one of the first names on Gordon Brown's Cabinet list, will tomorrow stand at the Dispatch Box in the House of Commons and fight for his immediate political career. In the Iran hostages affair, where 15 sailors and marines were held in Tehran for 13 days and then on their return given permission to sell their stories to the media, Browne is being lined up as the political fall guy for the evident error that saw a six-figure sum handed over to a hostage "heroine" and a young sailor selling his tearful story in the same week as four coffins returned from Iraq to British military bases.

With the Ministry of Defence first saying it had allowed the media sales - which saw Rupert Murdoch's News International and ITV's Tonight with Trevor McDonald programme pay £100,000 for the story of Leading Seawoman Faye Turney - then admitting it had changed its mind, subsequently banning all future deals till it completed a quickly ordered review of its media policy, Browne found himself in the middle of a political furore that saw opposition MPs branding the government incompetent and inconsistent and others saying the morale and reputation of Britain's forces had been ruined in a display of political insensitivity.

Intheinconsistentexplanations which have followed the release of the 15 hostages, newspapers critical of the sale of the stories have denied that they lost out in the bidding process, with the Daily Mail denying it offered £100,000 after Turney said she had "chosen" to tell her version of the events in Iran to The Sun. The Daily Mirror secured the tale of the youngest hostage, Arthur Batchelor, who recounted being held in solitary confinement and crying like a baby alone in his cell.

Despite the prime minister having his chief foreign policy adviser, Sir Nigel Sheinwald, go above the authority of the foreign secretary, Margaret Beckett, to secure a deal that would bring the 15 hostages back to British soil, Downing Street maintained this week that Tony Blair knew nothing of the background deals being hatched by the Royal Navy that would reverse the military tradition of not being allowed to sell stories.

The MoD maintains it was the Royal Navy's decision to allow the sales. And Des Browne's account is that he was simply told of the Navy's decision, accepted it, thought it over a weekend and then decided he didn't like their analysis as to why it was acceptable to allow chequebook journalism to do active service inside the Navy.

If there was rulebook inside the MoD that governed who held the power to make the final decision on paid media work, there are two possibilities: either Des Browne wasn't aware of any rule, didn't know what power he held and made a mistake in allowing the Navy to call the shots; or he was aware of the rule book, knew exactly the limitations of his influence, but accepted the Navy had greater fire-power that it could only have gained by first seeking out the authority of a power beyond Browne - in other words, that the decision was rubber-stamped by Number 10. This is an accusation Downing Street categorically denies, insisting the first the prime minister knew of the selling of stories was when he picked up his newspapers last Sunday morning.

The atmosphere in the Commons tomorrow will be akin to a trial. At stake is Browne's current Cabinet post, a role inGordonBrown'sCabinet,anda reputation as a safe pair of competent hands. All could evaporate if further explanations don't add up.

Browne,withapre-Commons background as an Ayrshire lawyer, is not regarded as an experienced operator in the desk warfare that exists between chiefs of the armed forces and their ministerial bosses in Westminster. But he is respected, knows when to take advice and when to consult on issues beyond his everyday knowledge. He has thrived, as one fellow Labour MP notes, "as a competent, not as a showman. Des may not know all the rules, but he knows who does."

In the Commons tomorrow he may need competence and showmanship to insist either he was not out-manoeuvred by the Royal Navy, or that he made a genuine error of judgement but one he thinks does not merit his resignation. But if the missing element in all the explanation - namely the influence of Number 10 - is cited by opposition MPs asthetruestoryofwhatreally happened, the loyal Browne is unlikely to point to Blair to save his own career.

Browne's first task in the Commons is to explain why he evidently adopted a submissive role and allowed the Royal Navy to take the crucial decision to allow the sailors to sell their stories. Did Browne know he had the power to overruletheNavy'scommander-in-chief naval home command, the second sea lord, Vice-Admiral Adrian Johns? Johns, based in Portsmouth, is responsible for all naval personnel and shore establishments. He flies his rank's flag onHMSVictory,theworld'soldest commissioned warship, in its dry dock.

When he needs, Johns can surround himself with all the pomp and tradition that Admiral Nelson enjoyed aboard the Victory. But Johns is no naval fossil and heknew,astheIraniansturned hostage-taking into a propaganda TV show, that the Navy had to respond.

Johns and advisers close to him are said to have believed that only the detailed personal stories of those held could counter the propaganda victory enjoyed by President Mahmound Ahmadinijad when he released the 15, saying it showed Muslim compassion against the insensitivity of the Navy that had allowed a woman to be on the front line instead of at home with her daughter.

The vice-admiral is believed to have regarded any Navy choreography of the captives' stories as likely to backfire. After the release of the 15, Johns said: "We thought it very important to let these people tell the story in their own words and through the media."

But that could have still happened without cash being handed over: when the media were invited to Portsmouth, six of the captives were present, allowed to give television interviews and field questions. Turney was not one of the half-dozen at the base, because her story had already been sold. But all 15 could have been questioned on a one-to-one basis, the stories coming in their words, their way. But ahead of the group's release, the Navy in Portsmouth had decided that was not how they were going to score points and get back the credibility of their service.

DidPortsmouth,ratherthantheMoDin Whitehall,havethe power and authority to do it their way? Would Des Browne - who even if he didn't know the extent of his power could find a civil servant lawyer who could tell him - allow the Navy to call the shots over the heads of his own press advisers? The Commons will want answers to these questions and more tomorrow.

IftheConservativesget their way, there will be hints from the government of a full inquiry.Thatcouldbethe compromisewhichallows Brownetostayandletthe witch-hunt cool off.

Johns would also be central to any parliamentaryinquiry.Educatedat Imperial College, London, he has served aboardsubmarinesandasaNavy helicopterpilotandinstructor,has commanded a number of ships and seen action across the world, notably in Iraq in 2003. But his inner knowledge of the MoD is also formidable. He has served as assistant director of naval operations; assistant director of warfare and assistant chief of naval staff before being promoted to vice-admiral in 2005 and his present post.

The Royal Navy's official rule book, The Queen's Regulations For The Royal Navy, will be as familiar to Vice-Admiral Johns as the offside rule is to a premiership referee. And the Commons will want to know what Johns and Browne discussed when it came to Chapter 68 of the regulations, which says service personnel should not receive payment for any media work they carry out in the course of their duties.

That looks clear enough: you are in the military and you cannot call a paper and sell your story. But there are grey areas: if Browne maintains that media fees earned off-duty - and the hostages were on compassionate leave when theysoldtheirstories-somehow slipped through a legal loophole, the Commons will erupt in disbelief.

Instead, what Browne will need to explain is why he did not take the lead role and discover from his communicationsstaffwhatanymedia-savvy individual would know: that this rule change would be a disaster-in-waiting.

Browne might also have to explain why the Navy decided to encourage the sale of the stories. One suggestion is that Johns and some other senior naval officials believed that if the rules of the market were left free, the Navy could not be accused of interference and so could not be accused of fighting Iranian propaganda with British propaganda. Believable? Browne can offer his side of events and so far this doesn't add up.

In an interview last week, Browne said: "A note indicating the decision and the analysis of the regulations that supported that decision came into my office on Thursday and early on Friday afternoon one of my officials took me through that. I was asked to note that decision." Browne is crystal clear here: he wasn't being asked what he thought, he was being told by the Royal Navy in Portsmouth what their decision was, ie, the stories would be told and they would sold. Browne's accounts paints himasasubmissivefigure.That, however,isanunlikelyscenario: Browne may be inexperienced, but he is not a naïve junior politician.

Theexplanationsuggeststhat Portsmouth,intheshapeofVice-Admiral Johns, believed Browne could not overrule their decision. But for a formerheadoftheArmy'spublic relations operation, this doesn't quite ring true: David Ramsbotham, now a crossbench peer, last week said that in hisexperience"everythingofsome magnitudelikethis"wasalmost routinely referred to Number 10.

Browne had a couple of days at home in Scotland to think over the decision the Navy had just taken. Back in London he would have been made aware of the warnings given by the Press Complaints Commission (PCC) that the release of the 15 hostages in Iran would require careful handling. Two emails were sent to the MoD, but nothing was sent back which acknowledged their concern.

The political reality is the PCC's fears were shared by some inside the MoD mediaoperation,amongthemthe director of news and press secretary to Browne, James Clark.

Clark's wife is Gaby Hinsliff, political editor of The Observer. Even if Clark was unsure how the story of the released sailors selling their stories for cash while the rest of the UK's armed forces risked their lives on routine services pay would come over, Hinsliff could have offered a few words of warning. Clark talked to Browne and the two are said to have shared a joint concern.

What Browne will also need to tell the Commons is whether he knew he had to the power to overrule Vice-Admiral Johns in Portsmouth and put the MoD in Whitehall back in the driving seat.

Brownehasadmittedawaveof discomfortpassedthroughhim:"I thought about the decision to sell the sailors' stories and over that weekend I acceptedtheanalysisthatwasput forward to me by the Navy, but I wasn't content with it."

In the Commons tomorrow Browne will need to stop talking in code, explain why he wasn't happy and open up. DavidCameron,theConservative leader,isexpectedtofocusinon Browne'suncertaintyandwhatlay behind it. The Tories smell the scalp of a rarebeastfromtheBlairyears:a genuine Cabinet resignation.