Instead of deciding when to watch the evening news, terrestrial viewers must take it at 10pm.

It is our time and we look forward to reclaiming it

News at Ten presenter, Trevor McDonald

And the chance to watch both bulletins - for the really keen - will be removed.

Yet some say the move could increase news audiences overall, helping buck the trend of recent years.

ITV's bulletin is on an hour earlier than it has been, when more people are available to view.

And neither bulletin now has to face such ferocious competition on the other major channel.

Instead of competing with huge ITV ratings-winners like Inspector Frost or Who Wants To Be A Millionaire?, the BBC Ten O'Clock News will be facing News at Ten on three nights a week.

And ITV's news - which was moved to 11pm because so many viewers were switching away from the 10pm bulletin - will also be more protected.

McDonald: 'Delighted'

Yet inevitably attention will focus on which bulletin performs better - in ratings and in news coverage.

Both sides are bullish.

Traditionally, News at Ten and its presenter Trevor McDonald got more viewers than the old BBC Nine O'Clock News.

"I'm delighted to be back in the 10 o'clock slot," he said.

"It is our time and we look forward to reclaiming it."

Inheriting millions of viewers from Who Wants To Be A Millionaire? and Peak Practice this week will be no handicap.

The size of a news bulletin's audience is heavily dependent on the programmes that precede it.

We want to be more ambitious than ITV, with more specialist correspondents, a broader agenda and more intelligent coverage

BBC's head of television news, Roger Mosey

But the BBC is confident too.

It points out that the new News at Ten is shorter than the old - 20 minutes, including advertisements - and that it is at 10pm on just three days in the first week.

"They don't seem wholehearted about it," said the BBC's head of television news Roger Mosey.

"The BBC Ten O'Clock News is a 32-minute bulletin, including regional coverage - and we want to be more ambitious than ITV, with more specialist correspondents, a broader agenda and more intelligent coverage."

Inevitably, the journalistic rivalry will be intense as the bulletins go head-to-head.

Some fear there could be a "news war", with a frantic search for sensational exclusives.

Smith: Criticised the BBC

The 10pm slot is ideal for pre-empting the following morning's newspapers - and stories that have been embargoed for publication the next day.

The irony is that most viewers will not be comparing the rival bulletins, because they will be on at the same time.

But journalists, spin-doctors and other professional media-watchers will - and so will the BBC governors and the culture secretary Chris Smith.

Last autumn, he welcomed ITV's move to 10pm and criticised the BBC's, blaming the corporation for the head-on clash - even though it announced its move first.

Politically sensitive

That makes the outcome of the battle politically sensitive.

The BBC insists it is going to judge the success of its news move over a couple of years, not a couple of weeks.

It hopes its other changes to BBC One - including a fourth EastEnders and investment in new dramas and comedy - will kick in this autumn, bolstering the news audience.

But others are likely to judge the outcome more quickly.