The Green Party’s manifesto sets out the party’s intention to tax the top 1%, as part of an overhaul of the tax system, and raise up to £70 billion for public services.

Co-leaders of the party Adrian Ramsay and Carla Denyer pledged to “mend broken Britain” at the manifesto launch event in Hove on Wednesday.

Under the party’s plans, a tax on multimillionaires and billionaires will be used to raise additional revenue to fund improvements to health, housing, transport and the green economy.

The Institute for Fiscal Studies (IFS) said the manifesto proposals will come with a “real economic cost” and increase disincentives to work, in addition to claiming the pledges would not raise as much money as expected.

The manifesto pledges to raise the national insurance rate to 8% on annual wages above £50,270, and bring in a wealth tax of 1% annually on assets above £10 million and of 2% on assets above £1 billion.

Along with other tax measures – such as removing the upper earning limit that restricts the amount of national insurance paid by high earners – the party estimates it could raise additional revenue of between £50 billion and £70 billion.

Ms Denyer said: “At the heart of this would be a tax on the very richest, the top 1% of people, requiring them to pay a bit more into the pot.

“From the Tories and Labour, we’ve been hearing a race to the bottom on tax.

“They think two pence off here and a penny off there will impress voters and they think that people won’t cotton on that this means even more devastating cuts to public services like the NHS that we rely on every day.”

The Greens have previously promised to spend £50 billion per year on health and social care by 2030, and to protect the climate for future generations and “bring nature back to life”.

Mr Ramsay said at the party’s manifesto launch that the climate crisis has been “pretty much absent from this election campaign so far”.

The party has pledged to stop “all new fossil fuel projects” in the UK, and cancel recently agreed ones such as Rosebank.

He said: “The other parties are running away from their promises on climate. Only the Greens understand that the solutions to the climate crisis are also the solutions to the cost-of-living crisis.

“The climate crisis is the most serious we face as a global community. Our commitment to you is that protecting our climate and nature lies at the heart of all of our policies.”

Mr Ramsay added: “We would stop all new fossil fuel projects in the UK and cancel those that have been recently licensed like Rosebank.

“We would be more ambitious than any other party when it comes to renewable energy, investing to ensure that our energy can come from wind and solar power. A secure energy supply and action on the climate crisis go hand in hand.

“Our investments in public transport, supporting the switch to electric vehicles and homes heated without fossil fuels means we would put this country on the path to being net zero years ahead of other parties.”

Elsewhere, the party proposed a frequent-flyer levy, a rise in the minimum wage to £15 and renewed its pledge to abolish tuition fees.

The manifesto also vows to disband the “dysfunctional” Home Office and replace it with a new “Department of Migration” – separate from the criminal justice system – as part of commitments for fair treatment towards migrants and valuing the “contributions” they make to British society.

“We want to be welcoming, promote social cohesion and support migrants to put down roots,” the document said.

On the party’s plans to abolish immigration detention centres, Mr Ramsay said: “We’re talking about giving people accommodation in society, rather than being in a detention centre.”

On defence, the party would maintain spending at 2% of GDP, but Mr Ramsay argued that nuclear weapons are an “outdated system”.

“We need to make sure that the money we’re putting into defence is used effectively on personnel, on the great work that our Army does for humanitarian work around the world and which we can continue to step up,” he said.

A Green Economic Transition plan is also included in the manifesto, which would aim to upgrade homes across the UK to increase their energy efficiency.

Opening the manifesto launch, Brighton Pavilion candidate Sian Berry said that as a renter herself, ending the housing crisis is a “top priority” for the party.

The party has promised to provide 150,000 new social homes every year and a “fair deal for renters” by giving powers to local authorities to introduce rent control measures.

Asked whether the party would consider building on the green belt to achieve its housing target, Ms Denyer said the 150,000 social homes a year by the end of the parliament would come from a “mixture of building and buying from the private sector”.

The IFS said the party’s proposal to restrict income tax relief on pension contributions would hit nurses and teachers, although its deputy director Helen Miller described some of the plans, such as closing loopholes within inheritance tax, as “sensible”.

Ms Miller said: “While some of the measures are targeted at the wealthy, the effects of the package would be much broader.

“Most obviously, it would be impossible to raise over £90 billion from taxing carbon emissions without the effect being felt by everyone.”

She added: “It is unlikely that the specific tax-raising measures they propose to help achieve all this would raise the sorts of sums they claim – and certainly not without real economic cost.”

Mr Ramsay said the party is “realistic” that it does “not expect to form the next government”.

He said: “When the Conservatives are booted out of Number 10 on July 4 and Labour take over, we plan to be there in Parliament in greater numbers to speak up for you on the issues that you care about.”

Mr Ramsay added: “Because with more Green MPs in Parliament, we will push Labour to stop backtracking on their promises.”

Ms Berry confirmed that four party candidates had been de-selected because of antisemitism allegations.