Hamilton has finished on the podium in his first three Grands Prix

The 22-year-old Englishman became the first driver to finish on the podium in his first three Grands Prix when he came second in Bahrain on Sunday.

And Stewart told the BBC he could usurp team-mate Fernando Alonso as champion.

"It's not inconceivable it could be done this year because McLaren look like the team to beat. If not, expect it within the next three," he said.

Interview: Motor racing legend Sir Jackie Stewart

"He is, of course, driving for one of the best teams in the world at the present time, with a competitive car, but nevertheless he's been able to accomplish more in a shorter time than any driver I've ever seen enter Formula One."

Hamilton's third place in Australia made him the first debutant to finish on the podium since Jacques Villeneuve was second to Williams team-mate Damon Hill in Australia in 1996.

Not to be making the kind of mistakes that new drivers usually make is a remarkable achievement Sir Jackie Stewart

He followed that up with second in Malaysia and his runner-up spot behind Ferrari's Felipe Massa in Bahrain leaves him tied on points with Spain's Alonso and Finn Kimi Raikkonen at the top of the world championship with 14 rounds left.

No driver has won the title as a rookie, barring the inaugural world championship in 1950, and Stewart says Hamilton is likely to make some mistakes in the future.

But the Scot insists that Hamilton could be a world beater for years to come.

"It's no easy matter getting into Formula One and attacking the great talents that are out there," Stewart told Radio Four.

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"For a new driver to do that with such consistency and not to be making the kind of mistakes that new drivers usually make is in itself a remarkable achievement.

"It's not unusual for a driver to do very well in his first year and have a bit of a dip in the second year. That's par for the course.

"But I think within the next three years, Lewis Hamilton will certainly be in contention and could easily win the world championship."