Win or lose, England’s much-loved all rounder Andrew Flintoff will get a rapturous reception from the crowd at the Oval ground in London as he plays what he insists is his final five-day test match, starting Thursday.

That much is certain. Little else about the match is. It starts with England and Australia in apparent equilibrium in their Ashes series at one victory apiece with one to play. That appearance of balance conceals huge fluctuations of fortune during a series that has seen at least two significant shifts in momentum.

The force certainly looks to be with Australia, following its resounding victory in the fourth test in Leeds to level the series. The same, though, was said last month as the action moved from the first test at Cardiff, Wales, where Australia dominated for four and a half of the five days, to Lord’s, where England had not beaten the old enemy since 1934. England won the Lord’s test.

Bets may not be off — there has been a reminder of cricket’s vulnerability to match fixers in reports this week of bookmakers’ approaching Australian players — but few can be laid with any certainty.

Australia has the advantage that, as holder, it need only draw to retain the fabled Ashes trophy. England has to win.

That does not mean that Australia will go out seeking a draw. That is tough to do over five days, potentially self-defeating and alien to the attitude of most Australian cricketers. It does mean, though, that it has more options in a close contest and will be less upset by rain delays.

Any repetition of the strangest spectacle of the corresponding match in 2005 — the Oval is the traditional venue for series finales — is unlikely. Then, with England desperate to secure the draw that would give it the Ashes after eight consecutive series defeats, spectators cheered rain delays.

England will need every moment it can get of the scheduled 30 hours or 450 six-ball overs of play. It will, though, cheer what often precedes a rain delay: heavy cloud cover.

Scientists tell you that there is no logical reason why a cricket ball should swing more with clouds overhead. Yet it undoubtedly does. This is where physics meets metaphysics.

During the opening test at Cardiff, a recent Australian bowler said that its players liked batting against the England paceman Jimmy Anderson.

His bowling came on to the bat at the right pace and was wont to leave it still more rapidly in the direction of the boundary ropes.

That was a fair reflection of Anderson’s performances against Australia, both in the series down under in 2006-7 and at Cardiff, to that point. At Lord’s, under heavy cloud cover, they found out why England goes on picking him. As the injured England batsman Kevin Pietersen pointed out in a radio interview: "If the ball is swinging both ways at 90 miles per hour, batting becomes a guessing game."

Australia guessed wrong a lot of the time, was bowled out cheaply and lost at Lord’s. The same happened again in the first innings in Birmingham where Australia had to battle to save a draw.

Under clear skies in Leeds, Anderson was back to being cannon fodder. His teammate Graham Onions varies similarly, if less drastically, in menace according to the conditions.

Australia’s designated swinger, Ben Hilfenhaus, has been, across all four tests, the best bowler on either team.

Each team has a selection conundrum over spin. Australia’s Nathan Hauritz has far exceeded expectation in the three matches he has played, but all four Australian seamers performed well in Leeds and could keep their places.

England will consider adding Monty Panesar to Graeme Swann. Panesar, a former national icon, is struggling for wickets, but may introduce control that England has lacked with the ball.

England has already made one big decision. It is giving Jonathan Trott his debut in place of the out-of-form Ravi Bopara. That decision made sense, but promoting Ian Bell into the difficult No.3 spot in the order that Bopara occupied is a gamble. Bell’s problem was beautifully summarized by the writer Paul Weaver: "The only time he does not look like a test-match batsman is when he is playing in one."