Theresa May will use a major speech to stake her boldest claim yet to Labour’s mantle as the party for social justice, promising that the government will tackle “everyday injustices” affecting working-class Britons.

In an address to the Charity Commission on Monday, the prime minister will pledge to build “a shared society” that respects the “bonds of family, community, citizenship and strong institutions”.

The broad-ranging speech is likely to be seen as a bid to deflect allegations that May’s government is too distracted by Brexit to pursue a coherent domestic policy agenda, as well as a further pitch to voters who feel they are “just about managing”.

She is expected to say: “The shared society is one that doesn’t just value our individual rights but focuses rather more on the responsibilities we have to one another. It’s a society that respects the bonds that we share as a union of people and nations.

“The bonds of family, community, citizenship, strong institutions. And it’s a society that recognises the obligations we have as citizens – obligations that make our society work.”

Though May’s move to brand her social justice agenda as “the shared society” has obvious parallels with her predecessor David Cameron’s oft-derided “big society” initiative – envisioned as a way to put people in control of local services and generate social cohesion – the prime minister is expected to present her own agenda as a definitive break with past policy.

Criticising previous governments’ supposedly disproportionate focus on the poorest in society, she will say: “It means making a significant shift in the way that government works in Britain. Because government and politicians have for years talked the language of social justice – where we help the very poorest – and social mobility – where we help the brightest among the poor. But to deliver the change we need and build that shared society, we must move beyond this agenda and deliver real social reform across every layer of society so that those who feel the system is stacked against them – those just above the threshold that attracts the government’s focus today yet those who are by no means rich or well off – are also given the help they need.

“Because people who are just managing, just getting by, don’t need a government that will get out of the way, they need a government that will make the system work for them. An active government that will … allow them to share in the growing prosperity of post-Brexit Britain.”

Her address represents an attempt to shift the political debate to relatively safe ground for the government, which has faced a week of intense criticism over its Brexit strategy and its response to the resignation of Sir Ivan Rogers, the UK’s representative in Brussels.

In a sign that the government’s honeymoon has ended, May was called “Theresa Maybe” and compared to her predecessor Gordon Brown in the right-leaning Economist magazine.

Her speech will revisit popular themes from her centrist pitch for the Tory leadership – such as reducing inequality and cracking down on tax avoidance and unscrupulous corporate practices – and will also reject “laissez-faire liberalism” and set out an interventionist strategy.

Outlining her plans for a “new philosophy that means that means government stepping up” above and beyond the remit of the traditional welfare state, May will signal her intent to divert government resources to helping families who are “just about managing”. She will tell the Charity Commission that her government will go “further to help those who have been ignored by government for too long because they don’t fall into the income bracket that makes them qualify for welfare support”.

The chancellor offered modest giveaways to such families in his autumn statement in November, including an increase in the tax-free personal allowance and a freeze on fuel duty.

The PM’s bid to renew her social reform agenda was immediately criticised by Tim Farron, the Liberal Democrat leader, as an attempt to distract from Tory struggles over Brexit. “This government is a complete and utter shambles and has no cohesive agenda. All it seems to do is jump from one Brexit crisis to the next”.