Jason Gillespie considers Andrew Flintoff and Kevin Pietersen as the biggest threats to Australia's Ashes chances in England.

The first Ashes Test starts in Cardiff on Wednesday. Gillespie also said that Australia cannot afford to take fringe players like Ravi Bopara and Graeme Swann lightly.

"They had Ashley Giles in 2005 who did an under-rated job and played on the Australian egos a little bit," Gillespie was quoted as saying in 'Adelaide Now'.

"I know Australians think that it was negative cricket the way Giles bowled to right-handers but it was effective.

"Now, Swann has been bowling pretty well. To give him credit, he has been good for England," the former Australian pacer added.

Gillespie urged the visitors to be on guard against Pietersen and Flintoff.

"They are two top-gun players and the England management will certainly be doing everything in their power to ensure they are fit and raring to go," said Gillespie, who took 259 wickets in 71 Tests for Australia.