The second series promises "shocking revelations"

According to initial overnight figures, the action-packed show narrowly beat Trial and Retribution on ITV1, which drew an audience of 5.5m.

But viewing figures were well below those of the last series, which averaged 6.8m viewers.

Starring John Simm, Life On Mars tells the story of a modern-day policeman who finds himself transported to the 1970s.

The current series is also the last, and viewers will find out how Simm's character, Detective Inspector Sam Tyler, became stuck in the past.

Producers have promised a "natural and explosive climax", but have filmed two separate endings "to keep everyone guessing".

"We're delighted that so many people returned to 1973 to enjoy Life on Mars," said a BBC spokeswoman.

Around 750,000 turned over to BBC Four after the programme finished to watch the next episode, she added.

The first series of Life on Mars was broadcast last year.

It was a hit with critics and audiences alike, and won an international Emmy award for best drama series.