Glenn McGrath says England's belief in themselves will be a major factor in deciding the outcome of the Ashes series, which starts at Lord's on Thursday. McGrath, Australia's top strike bowler with 499 Test wickets, concedes England appear more assured this summer, although he cautions that they may have taken a dent in last week's defeat in the third and final one-day international at the Oval.

"Their self-belief has definitely advanced," he said. "They are a lot more confident and are playing better as a team. They have had a lot more success over the last 18 months. Whether they truly really believe they can beat us we will have to wait and see."

It will be an intriguing series of the two best teams in the world. Australia are the top-ranked Test nation, having lost only twice [both to India] in their last 20 Tests; England are second and have also fallen only twice in their past 20 Tests while winning five series in a row. But, more tellingly, England have lost the last eight Ashes contests and are hoping to stop the Aussies from notching up No. 9. McGrath, who was rested for the tour match against Leicestershire, has already sensed the erosion of some of the swagger with which England started the summer.

McGrath warns that every member of the England team will have to be at his best if they are to stand a chance of competing with Australia. He still doubts whether the hosts truly believe they can beat the world champions for the first time since 1987. He has noticed that the England atmosphere under Michael Vaughan is different to that which prevailed when Nasser Hussain was captain - but he does not expect a different outcome to the Ashes.

Singling out his opposite number Steve Harmison as key to England's chances, McGrath makes it clear England can afford no loss of form from the Durham fast bowler - or anyone else. "In South Africa [last winter] I thought England had a far better team and should have beaten them easily ," he said, "but Harmy didn't perform as well as I thought he would. Matthew Hoggard bowled pretty well, and that helped them out. They won't get away with one or two key guys not performing this series. If that happens then I think we'll win and win well. They still rely on a few guys too heavily - the openers, for example - and for them to have any chance in the series they have to all perform in this series."

The Aussies have plans in place for England's opening pair Marcus Trescothick and Andrew Strauss. McGrath, mindful of his initial task to try to part the pair, is confident. "We hadn't seen a great deal of Straussy," he said, "so it was good in the one-dayers to get a bit more of a look at him and how he plays and think up a few more plans. We're pretty happy there. "Tres" is always the same. He doesn't really move his feet but he's got a pretty decent eye - so our plans won't be too different to them to what they've been in the past.

"To me body language is the biggest key, and that is one thing Australia does so well. During the last two one-dayers it was quite obvious to see that England's body language has dropped - it was terrible. That to me is a sign that it won't take much to get on top of them for it to really quieten down. It's easy to get yourself going and be aggressive when things are going well. To date they haven't shown any of that when they've been under the pump, and I think that's the time for a true team to really lift and turn things around."