By Nick Assinder
Political correspondent, BBC News website
David Cameron has stepped up his autumn offensive, slapping down his critics as insignificant and launching his big idea to mend the "broken society".
In dismissive remarks aimed at the likes of dissident Michael Ancram - who has urged him to return to core Tory values - Mr Cameron again signalled he is not going to give in to demands from Tory right-wingers for a change in direction.
Mr Cameron says it is a national service for the 21st Century
But the "national citizen service" has just the sort of ring to it that might appeal to the likes of Mr Ancram and others on the right of the party.
It hints at something like the old military national service, undertaken by every youngster, much admired by many Tories and many others who believe it broadened individuals' horizons, helped them into the adult world and instilled a sense of self-respect, discipline and responsibility.
Mr Cameron's big idea - on which he says he is prepared to see a Conservative government judged - is, he says: "As important to me as the manifesto. This to me is absolutely central to what I want to do for and with this country."
"Every 16-year-old should do this as part of growing up, part of becoming an adult," he said.
The Conservative leader believes his proposal to encourage all 16-year-olds to spend a summer holiday undertaking a number of projects ranged from military training to mountain climbing will help give them a sense of worth and a place in society.
And that, he believes, will start getting to the root of the problems which have led to what he has branded the "broken society".
Critics immediately pointed out, however, that the scheme would be voluntary and that there are already similar projects, such as the Duke of Edinburgh's Award, which youngsters can undertake.
Mr Brown launched his own voluntary scheme last year
They claim the sort of youngsters most likely to be involved in drugs, gun crime and violence are exactly the sort who will not volunteer to undertake the service.
Mr Cameron said he had been in favour of making it compulsory before being persuaded to make it voluntary - but said he may well take that step at some point in the future.
Instead, he wants to make it so attractive that every youngster will want to volunteer, he said.
However, the fact that it is voluntary means the idea has faced criticism for failing to be as radical as it might have been.
As 10 Downing Street swiftly pointed out, Mr Brown has already launched a youth volunteering project, called V, which had proved popular over the past year.
But Mr Cameron is hoping voters will accept his analysis and support the idea of a national citizen service and see it as an important statement about the direction he intends to drive policy on a key issue.
Whether it will help silence those "voices from the sidelines" of his own party remains to be seen.