Liberal Democrat leader Nick Clegg today called on David Cameron to apologise for a speech in which the Tory leader appealed for a greater sense of public morality.

Mr Clegg said Mr Cameron had effectively claimed that if people were out of a job or struggling to make ends meet it was their own fault.

"If David Cameron has any decency he would apologise to the people of Glasgow East for the arrogance of his comments," said Mr Clegg during a visit to the city.

The Liberal Democrat leader was campaigning in the constituency where nominations close this afternoon for the by-election caused by the resignation on health grounds of Labour MP David Marshall.

Labour is defending a 13,500 majority over the SNP, which has claimed a political "earthquake" is under way.

Mr Clegg's attack on the Tory leader came after a speech which Mr Cameron made in the constituency on Monday.

Mr Cameron appealed for a greater sense of public morality, saying politicians were too afraid to say what was right and wrong.

In the most controversial section of his speech, the Tory leader said: "We talk about people being at risk of obesity, instead of talking about people who eat too much and take too little exercise.

"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."

Mr Clegg, who began his campaign visit with a tour of a Scottish Gas training facility in the constituency, said the area had been neglected for "generations" by Labour, while the SNP wanted to treat voters as "pawns" in a political game at Holyrood and Westminster.

"You are certainly not going to get any hope from the Conservatives, whose leader had the arrogance to come here just recently and tell you that even if you are struggling on benefits, struggling to make ends meet, struggling to find a job, struggling to cope with poverty, that it's your own fault and he won't lift a finger to help you."

Mr Clegg went on: "I think there is no excuse in politics for the lucky and the privileged to show such contempt for the poor and the forgotten."

He also attacked Labour, saying the constituency had been neglected by a Government that was "increasingly pointless", led by a Prime Minister who was also increasingly pointless.

"I think Gordon Brown's political credibility is almost entirely evaporated already," said Mr Clegg.

"If he cannot hold on to a seat which for generations has been synonymous with the Labour Party I think he will pretty well have forfeited any remaining credibility he has with the people of Glasgow, Scotland, and Britain."

Mr Clegg said the Liberal Democrats, who came in third place with 11.9% of the vote in 2005, offered the politics of hope.

Elsewhere on the campaign trail, Labour and the SNP clashed on law and order.

The Nationalists, fielding candidate John Mason, said crime had fallen by up to 24% in the constituency and called for Labour to back action to tackle the problem of airguns and reduce access to cheap drink.

They also highlighted plans for recruiting an extra 1,000 police in Scotland.

Mr Mason said: "The SNP has a record of success in this constituency after only 12 months in government in training more police for our streets, tackling the gangs, reducing knife crime and bringing forward radical proposals to target the cheap booze culture that fuels much of the violence in our communities."

But Labour's Margaret Curran said much of any improvement was attributable to past efforts by previous administrations in areas such as anti-social behaviour, and she unveiled her own five-point plan to tackle crime.

One element of this plan was doubling the number of extra police on the streets in the city's east end, she said.

"The council has paid for 20 extra police because the SNP broke their promise on recruiting extra officers," she said.

"I want the council to double this figure in two years and will fight until they do."

Other elements of her action plan included getting police out of cars and on to the beat, jail for those carrying knives, more CCTV in the area and for known drug dealers to be targeted by police.

Polling takes place on July 24 in a by-election which is also being contested by the Tories, the Greens and the Scottish Socialist Party.