South African fullback Percy Montgomery says he will not be surprised if Tonga manages to upset England this weekend and send the defending champions out of the Rugby World Cup before the quarter-finals.

Montgomery has played against both sides in Pool play thus far and kicked 18 points in the Springboks' 36-0 thrashing of Brian Ashton's side.

"You can never write off the big teams like England because they have so much experience and they have the back-up," Montgomery said.

"I think it will tough for them. The Tongan team have got some good momentum at the moment, they've got some really good players.

"It wouldn't surprise me at all if they were to win. They have had a great World Cup, they are playing attractive rugby and it's a strange game.

"We needed all our composure to beat them and England will find it hard."

"Playing against the Islanders is always tough," Montgomery added.

"A lot of the Tongan team play overseas. They played with passion, they defended very well and attacked very well.

"We played with 13 men at one stage and it was quite difficult. The guys came off the bench and we managed to win and we got five points."

Montgomery admitted the narrow win came as a timely wake-up call and could be just what the side needed as it approaches the knockout stage of the tournament.

"It is always good to have a test like this, it brings you back down to earth a bit.

"Obviously we wanted a bigger score but this is test-match rugby. The days of beating teams by 70 points... I mean it doesn't work like that any more.