Jo Swinson has told voters that the Conservatives and Labour are “gambling with your future” over Brexit, as she launched a Liberal Democrat manifesto featuring significant spending and investment pledges, financed by what the party says would be an economic boost from staying in the EU.

Speaking at a launch event in a nightclub in north London, Swinson sought to present the Lib Dems as a clear alternative to the two main parties with a promise of more than £60bn extra spending a year in the next parliament, focused on areas such as schools, mental health and childcare.

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The party is also pledging £130bn in infrastructure spending, £80bn of which would go to environmental projects. The manifesto promises to introduce higher air passenger duties for frequent flyers, raising nearly £5bn a year by 2024/25.

A key sell in the Lib Dem manifesto is what the party calls the “remain bonus”, brought by higher GDP from cancelling Brexit and forecast to rise to £14bn a year over the parliament.

Swinson, who has taken a central role in a campaign marketing the Lib Dems heavily as the anti-Brexit party, leaned on this theme to introduce the manifesto, and again attack the Tories and Labour.

“There is no form of Brexit, that will be good for the future of our country,” she said. “[Brexit] would put our jobs at risk, hurt our NHS, reduce our environmental protections, threaten workers’ rights and it would make us less safe.

“Whether Brexit is done by Boris Johnson or sorted by Jeremy Corbyn, they are both gambling with your future.”

Swinson has sought to attract remain-minded voters from both the main parties, presenting herself as a possible prime minister. However, she faces some pressure in the remaining weeks of the campaign, with the Lib Dems having dropped to about 15% in the polls, and previous internal party expectations of up to 80 seats potentially won being drastically scaled back.

She told Lib Dem activists at the launch: “Don’t let anyone tell you that it doesn’t get better than Boris Johnson or Jeremy Corbyn, that we are destined to stand alone in the world, that we must face the biggest challenges on our own, that Brexit is inevitable. None of that is a given.”

The flight tax would be levied only on international trips and would not add to the costs of people who travel by plane only once or twice a year.

The bulk of the extra public spending would involve £10bn in additional money for schools, announced in advance, as well as more funding for health and social care, childcare and tackling in-work poverty.

A costings document released with the manifesto shows what the party says would be almost £64bn in extra government income by 2024/25, £14bn of which would be a net “remain bonus” – extra GDP balanced against payments into the EU budget.

The next biggest revenue earner would be almost £8bn from a 1p addition to income tax to fund social care and the NHS, with other money gained from returning corporation tax to the level of 20% (up from the general rate of 19%) and from amending capital gains tax.

The costings document shows the party expects revenues of almost £1.5bn a year in duties on cannabis and savings on law enforcement after it decriminalises the drug.

The £80bn of investment in green projects would include areas such as home insulation and sustainable transport. There is also an aim of spending 10% of the transport budget on walking and cycling.

Capital spending would be assessed on government balance sheets about how much “net worth” is added, allowing for greater spending within the same borrowing limits, which the party has pledged to keep to 1% of GDP a year.

Infrastructure projects would be assessed by an independent body as to whether they constitute value for money.

In extracts of the manifesto released overnight, the party promised to extend the scope of free school meals, increase schools spending by more than £10bn a year within the next parliament, and recruit 20,000 more teachers.