Rising costs, the disappearance of third spaces and reduced access to artistic opportunities are causing young people to feel “disconnected, isolated and locked out of creativity”, according to research commissioned by a youth arts charity.

The Roundhouse, a multi-arts venue in north London that reopened in 2006 with a focus on running youth programmes, has released the findings to coincide with the publication of its 20-year impact report on Monday.

It found that 87% of 18- to 30-year-olds believe they have fewer in-person opportunities to connect with others, build confidence and be creative outside school and work, compared with previous generations. Just over half of respondents pointed to a lack of safe community spaces, such as youth clubs, as one of the main barriers to forming connections with a community.

In a statement, the Roundhouse said that “young people are losing the environments that help develop the confidence, relationships and transferable skills needed to enter employment” and referred to the £1.2bn real-terms cut in youth service spending by English local authorities since 2010. It also acknowledged the higher rate of youth unemployment in London, 24.6%, compared with the national average of 14.6%.

Jack Rooke, the Bafta award-winning writer behind the Channel 4 series Big Boys and an alumnus of the Roundhouse, said: “When I look back at the start of my career, loads of the places that nurtured me and my ideas have vanished.”

Concerns over a “lost generation” of young people not in education, employment or training have gained greater attention after the publication of the first part of a government-commissioned report by the former Labour health secretary Alan Milburn last week. It cited structural issues, in addition to ill health and inequality, as factors responsible for official statistics showing the number of young people not working or studying has surpassed a million during the first quarter of this year.

Rooke said: “The Milburn review is tackling an urgent crisis in youth unemployment, but I believe it’s crucially important to look at the bigger picture. The crisis facing young people isn’t just economic; it’s deep, systemic isolation, low self-esteem and loneliness.

“Alongside employment, we should prioritise overall wellbeing by providing more physical spaces where young people can try new things, figure out who they are, what they might thrive in and just have some fun. It’s supposed to be fun to be young, we’ve all got to try and remember that.”

Other alumni have paid tribute to the Roundhouse’s work supporting more than 100,000 young people throughout the past two decades. Nabhaan Rizwan, a Bafta-nominated actor, spoke of the organisation as his “arts school” and Daniel Kaluuya, the actor who is the venue’s associate director, said: “I wouldn’t be here without the Roundhouse thinking differently, opening doors and truly backing ideas.”

The research also found that one in eight felt that creative opportunities were inaccessible due to their class or background.

Rooke, who developed his play Good Grief while a resident artist at the Roundhouse, said: “If we keep pulling up the ladder on community arts spaces and creative resources for young people, British culture will feel like one rather beige private school common room where all the stories sound the same. The same goes for state schools ensuring they keep encouraging young people to engage in arts subjects, even just for their own enrichment.

“Personally, I wouldn’t have a creative career without places like the Roundhouse, IdeasTap, Vault festival, BBC Switch or BFI Young Audiences Content Fund, believing in me and offering me space, mentorship and funding to make my early work. Creativity is crucial for many young people’s wellbeing and adjustment to adulthood and we cannot allow it to become a luxury reserved only for those who can afford it. And we can’t allow our future generations of artists, actors, writers and performers to not represent the rich width and breadth of communities in our country.”

Earlier this year, the Roundhouse joined with the Centre for Young Lives thinktank to launch the Young Creatives Commission in response to the government’s national youth strategy. The commission plans to publish a report in December that will include recommendations on placing arts provision on a par with sports and how to open more inclusive pathways into the creative sector.

Marcus Davey, the Roundhouse’s outgoing chief executive, said: “This research paints a worrying picture of life for many young people in Britain today. Too often, opportunities to build belonging, confidence and creativity are shaped by cost, postcode and access – and at a time when the government is rightly championing the growth of the UK’s creative industries, we must ensure no young person is left behind.”