Reform UK leader Nigel Farage has said he wants to make it easier for people to have children, as he confirmed his party would back more generous tax breaks for married people and scrap the two-child benefit limit.

In a speech in central London, Farage said he wanted to lift the cap “not because we support a benefits culture” but because it would make things easier for lower-paid workers.

If his party wins power, Farage said he would also reverse the government’s cuts which saw the winter fuel payment withdrawn from 10 million pensioners.

Responding to the speech, Labour Party chairwoman Ellie Reeves accused Farage of “fantasy promises”, which “are exactly how Liz Truss crashed the economy”.

Farage’s intervention comes as the prime minister faces pressure from his own MPs on government spending decisions, including cuts to disability benefits.

Some Labour MPs also want to see the abolition of the two-child benefit cap, which prevents most families from claiming means-tested benefits for any third or additional children born after April 2017.

Education Secretary Bridget Phillipson has said the government is considering lifting the cap but that it would “cost a lot of money”.

Last week, Sir Keir announced plans to ease cuts to winter fuel payments, but has not yet set out how many pensioners would see the payment reinstated or how it would be paid for.

During a wide-ranging speech, Farage also said his party’s “biggest aspiration” was to lift the salary level at which people start paying income tax to £20,000.

“These proposals are expensive but we genuinely believe we can pay for it,” he said.

He said the measures would be paid for by scrapping net-zero climate measures, stopping hotel accommodation for asylum seekers, ending diversity and equality initiatives in the public sector and cutting the number of quangos – bodies which are funded by taxpayers but not directly controlled by central government.

The Reform UK leader said removing the two-child benefit cap, which would cost an estimated £3.5bn, was “not a silver bullet” but would help families.

He said his party wanted to go “much further to encourage people to have children, to make it easier for them to have children” and added that was why his party would be pushing to make tax breaks for married people more generous.

He said he was “not moralising” on the subject of marriage, adding that his own “track record was not so good on this”, having been divorced twice.

However, he argued that “making marriage a little bit more important” was “the right thing to do”, as it gave children “the best chance of success”.

Currently married couples can transfer £1,260 of their personal allowance – the amount they can earn without paying tax – to a spouse or civil partner who earns more than them. This results in an annual tax cut worth £252 for some couples.

In addition to raising the personal allowance for everyone from £12,570 to £20,000, Reform are also proposing to exempt one partner in a marriage from paying tax on the first £25,000 of their income.

Stuart Adam, a senior economist at Institute for Fiscal Studies think tank, said increasing the annual income tax allowance to £20,000 could cost between £50bn and £80bn a year, depending on the details.

“As it stands, I don’t think they’ve really set out how they would pay for such big giveaways,” he said.

“Of course they don’t have to do that yet – we’re not at a general election. But at some point, if they’re going to be a party of government, they would have to make those numbers add up.”

Asked if he would commit to the triple lock policy – which automatically increases the state pension each year by the highest of price inflation, average earnings or 2.5% – Farage said it was not a subject the party had “addressed as yet” but promised it would before the next election.

Following the speech, Farage was also asked about his view on abortion limits. He replied that he was pro-choice but that it was “utterly ludicrous” for abortion to be allowed up to 24 weeks, when a hospital would “move heaven and earth” to help a baby born at 22 weeks survive.

Elections held at the start of this month saw Reform UK make big gains at the expense of both Labour and the Conservatives – winning one by-election and two mayoral races, as well as gaining 677 new councillors.

Farage spent much of his speech attacking Labour and making a pitch to the party’s traditional voters, describing Reform as “the party of the working people”.

He said the Conservatives had become an “irrelevance” adding: “They’ve had a good 200 years.”

Conservative shadow chancellor Mel Stride said: “Today Nigel Farage abandoned hardworking families who live within their means.

“He thinks taxpayers should pick up the bill for people on benefits to have whatever family size they choose. That simply isn’t fair or economically credible.”

Liberal Democrat leader Sir Ed Davey said Reform UK was making “huge unfunded spending pledges and only vague promises of fantasy savings”.