What has happened to Mitch?

From the loungerooms of Launceston to the Long Room at Lord's, no single issue has dominated discussion quite like Mitchell Johnson's plummeting fortunes in England. The conquistador of South Africa has been reduced to an erratic, unreliable bit-part player this week, placing tremendous pressure on his fellow bowlers and greatly reducing Ricky Ponting's options.

The world's third-ranked bowler was the third best paceman in the Australian attack on Saturday, and a distant one at that. Too short, too wide and too easily dominated by England's openers, Johnson left Ponting with few alternatives other than to withdraw him from the attack after just three overs in the hope Peter Siddle and Ben Hilfenhaus would prove less wasteful with the new ball.

Johnson was eventually redeployed in the 27th over, and hardly inspired confidence by spearing the second ball of his second over towards the slips cordon and only just within reach of an outstretched Brad Haddin. A burst from around-the-wicket went some way to straightening his trajectory, however, and Johnson, for the first time in the series, managed at least to contain England's batsmen over the course of a ten over spell.

That Australia was satisfied with Johnson merely tying up an end indicates the extent to which the situation has deteriorated. Johnson was brought to England to provide vigour and menace, not contain, and his lack of direction and form continues to be the most pressing concern for Ponting entering the final three Tests of the series.

So what precisely is the problem? How has a man who broke Graeme Smith's hands twice in three Tests become a bowler whose performances are best viewed through barely-splayed fingers? Is the slide reversible?

Three recurring themes have emerged from conversations with sources close to Johnson on both sides of the Australian camp. They are, in no particular order, a lowering of arm height, an attempt to bowl too quickly and a domestic situation in which Johnson's mother has publicly harangued his fiancée in the Australian tabloids.

The last of these issues is the most difficult to gauge in terms of its impact. A sensitive soul, Johnson has rarely, if ever, had personal issues aired in public, and his mother's inflammatory letter to a Melbourne newspaper just days out from the Cardiff Test can hardly have helped his state of mind. Johnson was, until recent years, known as much for his shy demeanour as his express bowling in Australian cricket circles, and the combined effect of a public squabble and the pressure of "spearhead" status in his first Ashes series cannot have been easy to manage.

The mechanical aspects of Johnson's bowling are easier to identify, though not necessarily to fix. Troy Cooley, Australia's bowling coach, has worked at length to restore Johnson's arm height over the past 18 months, and despite success in recent series in Australia and South Africa, a more round-arm release has set in.

A lower release point, even by a degree or two, can substantially reduce a left-armer's margin for error. A taller, more orthodox delivery arm should offer a paceman greater control of length, and lessens the likelihood of the ball spraying laterally. And in attempting to live up to his reputation as Austalia's bruiser-in-chief, Johnson has sacrificed swing for pace. Or so the theory goes.

These are not necessarily new problems. On tours of the West Indies and India last year, Johnson struggled for consistency, but in neither case was he bridled with the responsibility of leading the Australian attack. His man-of-the series effort in South Africa and elevation to the role of spearhead for the Ashes series - in which every triumph and failure is magnified - has delivered him to a plinth he has never previously occupied, and one that has left him exposed as form and confidence have deserted him. Anonymity is no longer a luxury he can count on.

But such discussions are of little help to Ponting in the immediate term. The Australian captain is in desperate need of a bowler who can penetrate the defences of England's best batsmen, and build pressure in partnership with the likes of Hilfenhaus and Nathan Hauritz. Johnson has failed in both regards to date. Figures of 3 for 200 from 38.4 overs - including no second innings wickets - tell the tale of a man struggling for control over his game, and Johnson's body language has too often resembled that of a downtrodden trundler rather than the modern day gladiator Ponting had counted on.

Assuming England declare their second innings closed early on Sunday, there is little Ponting can do to rectify the unmitigated disaster that was Johnson's outing at Lord's. Edgbaston is another matter, however. Despite stubborn attempts to maintain the fast bowling unit from South Africa, Australia's selectors will now be sorely tempted to reintroduce the reassuring presence of Stuart Clark and/or Brett Lee into the attack, but just who would make way remains a sizeable point of contention.

Without doubt, Hilfenhaus has been the pick of Australia's pacemen while Hauritz, playing through the pain of a dislocated finger on his spinning hand, has grown in stature with each innings this series. Peter Siddle has not been as evident in the wicket-column as his peers, but has interspersed several blistering spells between occasionally wild ones. On intimidatory grounds alone, he is worth persisting with.

That, then, leaves Johnson, who has done less to justify his place in the starting XI than Australia's other three frontline bowlers. Demotion from spearhead to outcast in the space of three Tests would be both stunning and difficult to envisage, given the faith placed in him by Andrew Hilditch's panel over the years, but in these desperate times little can be assumed.