BIRMINGHAM: England have not lost to Australia at Edgbaston in 18 years, but to preserve that record as the Ashes gets under way in Birmingham on Thursday, the hosts will need their middle order to fire amid uncertainty over their top three.

Having tried a number of different opening partnerships in recent years, Jason Roy, one of England's stars in white-ball cricket at the World Cup, has been fast-tracked into the test side.

He will almost certainly open the batting in Birmingham alongside Rory Burns, who averages less than 23 runs from his seven tests. Yet the uncertainty in the top order has been compounded in the days leading up to the first test, with Joe Denly, England's regular number three, having been pushed down to number four to make way for captain Joe Root.

Denly has enjoyed limited success, averaging 24.16 from six innings, and England coach Trevor Bayliss and Root have decided to shake things up.

"He (Root) rang me the other day and told me he wanted to bat three and for me to go in at four," Denly said on Tuesday. "I think Rooty just wanted to get involved in the game, get up there and get out in the middle."

Root averages 48 from 60 innings at number four -- compared with 40 from 40 innings at three -- but the captain's experience could be vital to bolster the largely untested trio of Roy, Burns and Denly, and set England up for their quality to come.

"It will come down to which team bats the best," former England assistant coach Paul Farbrace said. "England's middle order is so strong, and I expect them to get the majority of the hosts' runs."

The experienced Jos Buttler, Ben Stokes, Jonny Bairstow and Moeen Ali could bat in any order and it would not make much difference, with the potential of Sam Curran offering an additional option.

It would not be the first time England's strength in depth has come through, with Andrew Flintoff and Kevin Pietersen making match-winning Ashes contributions in 2005, while Ian Botham's famous 149 not out to beat Australia in 1981 came when batting at number seven.

Australia are likely to pit Cameron Bancroft, David Warner and Steve Smith together at Edgbaston for the first time since they were banned for their roles in the ball-tampering scandal in Cape Town last year, with Usman Khawaja batting at four.

Further down the order, though, there is less firepower, and less certainty as to who will come in.

"Whoever wins the Ashes, it is the contributions of batsmen five and six that will make all the difference," former Australia all rounder Brad Hogg said. "There are some headaches for Australia in that middle order."

Frontline England bowlers Jimmy Anderson and Stuart Broad have taken 1,019 test wickets between them, but World Cup hero Jofra Archer and Chris Woakes, fresh from career-best figures against Ireland, can provide further depth in the seam bowling attack.

Furthermore, both can bat, with Woakes averaging almost 30 in 45 test innings for England, while Archer's first-class average is over 30.

Those contributions lower down the order in what looks likely to be overcast, bowler-friendly conditions at Edgbaston, could sway a tight first test of a close-run Ashes series.