Fat or poor? It's probably your own fault, Cameron declares

The Tory leader, in an obvious shift of approach, claimed society had become too sensitive and scared to speak out about what was right or wrong, good or bad.

Speaking out against this 'moral neutrality', he called for a return to plain-speaking and took his own advice by stating people's social ills were often the result of their own actions.

Hardline: David Cameron with Davena Rankin, the Tory candidate for the Glasgow East by-election, left, and Leader of the Tory Party in Scotland Annabelle Goldie, right, during a visit to the Gallowgate estate in east Glasgow

'We talk about people being at risk of obesity instead of talking about people who eat too much and take too little exercise,' he said.

'We talk about people being at risk of poverty, or social exclusion: it's as if these things - obesity, alcohol abuse, drug addiction - are purely external events like a plague or bad weather.

'Of course, circumstances - where you are born, your neighbourhood, your school, and the choices your parents make - have a huge impact. But social problems are often the consequence of the choices that people make.'

He added: 'There is a danger of becoming quite literally a de-moralised society, where nobody will tell the truth anymore about what is good and bad, right and wrong.

'That is why children are growing up without boundaries, thinking they can do as they please, and why no adult will intervene to stop them - including, often, their parents.

'If we are going to get any where near solving some of these problems, that has to stop.'

Changing tack: The Tory leader says society should be less sensitive and realise some people who are poor, fat or addicted to drugs may only have themselves to blame

Mr Cameron unveiled his tougher approach in a speech in Glasgow, where he was launching his party's campaign for the Glasgow East by-election.

Gordon Brown's leadership is on the line over the vote in what is Labour's third safest seat in Scotland.

The Tory leader's strategy ends years where politicians have avoided making judgements on personal behaviour in case they backfired.

They are also by far his most strident comments on the issue of personal and moral responsibility.

'Refusing to use these words means a denial of personal responsibility and the concept of moral choice.'

Trying to see off any comparisons to his predecessor John Major's doomed 'back-to-basics' speech, he was quick to point out politicians were fallible too.

'Of course as soon as a politician says this there is a clamour - "but what about all of you?" And let me say now, yes, we are human, flawed and frequently screw up.

'Our relationships crack up, our marriages break down, we fail as parents and as citizens just like everyone else. But if the result of this is a stultifying silence about things that really matter, we re-double the failure.

'Refusing to use these words - right and wrong - means a denial of personal responsibility and the concept of a moral choice.'

Tory insiders said Mr Cameron was adopting a deliberately harsh line because he wants to gain support for taking hardline action against people who make the wrong choices.

In recognition of the growing concern over knife crime, he also promised to issue the courts with a 'presumption for prison' for those caught carrying a blade.