Former Conservative prime minister Sir John Major has criticised the “shocking” impact of inequality in Britain and said more needed to be done to urgently tackle the gap between the rich and the poor.

In a speech reiterating a number of touchstones of one-nation Conservatism, he pointedly set himself against language that sought to cast those who were out of work as “idlers” and benefit claimants as “scroungers”

Delivering a Hinton lecture entitled A nation at ease with itself?, Major told the audience in London that he had begun to reflect more and more on inequality as he grew older.

In a country now immensely more wealthy than the one in which he grew up, he said that life was still not easy for many, adding: “Even in areas that are recognised as wealthy, there are families or individuals who have fallen behind.

“Policymakers must understand how hard it is to escape from such circumstances. It is not inertia that keeps the unemployed immobile: it is simply that, without help, they are trapped.”

Turning to the role of the benefits system, he said: “Let us cast aside a common misconception. Everyone out of work is not an idler.

“Everyone in receipt of benefits is not a scrounger. Of course idlers and scroungers exist – and governments are entirely right to root out the cheats who rip off the taxpayer. But the focus must not be only on those who abuse the system; we need equal concentration on those who are failed by the system.”

Describing poverty as being “not only about empty pockets”, Major described contemporary Britain as one in which the lifespan of the poorest in some major cities was 20 years shorter than those of the most wealthy.

“I have no doubt that much of this disparity is caused by poor lifestyle, poor choices, poor diet – but poor environment, poor housing and poor education must surely be contributory factors. Whatever the reasons, this is a shocking situation in 2015,” he added.

The former prime minister went on to deliver a plea for the upgrade of Britain’s infrastructure, as well as emphasising the roles of the private sector and charities.

However, while talking of his pride in the scale of philanthropic, voluntary and charitable work across the UK, Major warned that a reality check was required, stating: “We cannot be complacent about our charitable sector. There are negatives: we have all seen the publicity generated by bad fundraising practices and poor governance.

“I won’t dwell on these shortcomings, except to note that all charities have a duty to protect their reputation. Unless they are seen as efficient and well run, donations will fall away.”