'Doctor Who' to remain earth-based

Doctor Who supremo Russell T Davies has cited budgetary constraints as the real reason for the Tardis's lack of trips to alien planets.

In an interview with Doctor Who Magazine, the writer claimed that creating unearthly landscapes is "hugely expensive" and would provoke strong criticism if carried out cheaply.

"The mockery we would get walking into a forest and saying that we're on the planet Zagfon!" he explained.

When the Tardis did land on alien territory last season it coincided with fewer viewers for the two-part story. But Davies was quick to explain that moving away from Earth - or a parallel version - was not the cause.

"'The Impossible Planet' and 'The Satan Pit' got our lowest viewing figures last series, but none of us is saying that therefore people don't like alien planets; I think that was just mid-summer heat, and lack of promotion, and a natural series dip."

The multi award-winning show will return for a Christmas special, followed by the third series in Spring 2007.