Shadow chancellor John McDonnell will claim that a Labour government would save families an average of £6,700 a year by “putting a stop to rip-off Britain” as the party narrows its focus to bread-and-butter issues.

With just over a week to go before polling day, McDonnell will on Wednesday say that Labour’s policy of tackling “profiteering monopolies” and “bad bosses” would benefit voters’ budgets.

“As Chancellor I want to ensure government has sound finances, but I want more than that. I want every family, every household in Britain to have sound finances,” he will say.

“That means putting a stop to rip-off Britain and making real change so that people are not powerless in the face of profiteering monopolies, bad bosses at work and cast aside by a government that just stands by.”

In a dossier to be published alongside the speech, McDonnell will claim that Labour policies including nationalising utilities and reducing the cost of rail season tickets would put £6,700 in the coffers of the average household.

Other Labour policies with a direct impact on voters’ finances are free childcare for all two- to four-year-olds, free prescription charges, and free school meals.

The speech is intended to herald a renewed focus on the cost of living in the final few days of campaigning.

Party strategists remain concerned about the challenge of holding on to leave-voting seats across the Midlands and the north, let alone advancing into Tory-held constituencies.

And many Labour candidates are privately concerned about the scattergun nature of their party’s manifesto giveaways, from broadband to rail tickets to restoring pension payments for Waspi (Women Against State Pension Inequality) women.

“The manifesto is good – it’s just long and confusing. You need a few targeted, short messages and keep repeating them,” said one Labour candidate in a leave-voting seat.

She added that some of Jeremy Corbyn’s policies appeared too good to be true – particularly among groups of voters who were already sceptical about him. “The only feedback I have had about free broadband is, ‘Does he think he’s Santa Claus?’” she said.

Another candidate in a Labour heartland seat complained about the manifesto. “There’s far too much in it, and it’s too randomised. It needed a narrative arc.”

Corbyn was attending a Nato reception at Buckingham Palace on Tuesday evening; but he is expected to spend much of the rest of the week criss-crossing the Midlands, where there are a number of target seats, as well as constituencies Labour hopes to hold on to.

Another candidate said the party had not bothered to include a promised rail fare reduction announced on Monday on their campaign Facebook page, because it was just likely to increase voter scepticism about whether the party’s programme is deliverable.

The Conservatives’ lead in the polls is narrowing, and Labour insiders said their own data from leave-voting seats had improved in recent days. They believe this is due to the lagged impact of the manifesto launch, and Corbyn’s competent performance in the BBC Question Time election debate last month.

But they acknowledged that the terrain remained challenging. Last week’s YouGov projection gave Johnson a comfortable 68-seat majority.

As well as having concerns about policies, several candidates in defensive seats said they had had minimal backup from Labour HQ, with much of party’s effort directed into trying to make gains.

Others complained that their paid-for mailshot, which is centrally administered by the party, had been delayed, arriving to households after postal voting forms. “If we lose seats like these, then we lose them for a generation,” said one Labour candidate in a vulnerable marginal.

Last week, Labour appeared to signal a shift in strategy towards wooing Brexit-backing voters in the Midlands and the north – but this appeared to have had little impact on the allocation of resources.

As well as promising to save voters money, McDonnell will on Tuesday highlight levels of deprivation and inequality in the economy.

“It’s three weeks to Christmas,” he will say. “This week the Channel 4 Dispatches programme reported on the reality of rising child poverty; a new Shelter report found 135,000 children will be without a home this Christmas; and an analysis by the Equality Trust shows the UK’s six richest people control as much wealth as the poorest 13 million. With children going hungry and homeless are we really living up to the values of Christianity or any other of our religions or beliefs for that matter?”