Labour has pledged to put “creativity at the heart of the school curriculum” in a series of policy announcements that coincided with a gathering of artists, actors, teachers and arts leaders convened by Prince Charles to address the subject.

About 200 people, including Benedict Cumberbatch, Vivienne Westwood, Lenny Henry, Andrew Lloyd Webber, Zoe Wanamaker and Meera Syal were at the Royal Albert Hall to support a campaign to promote the arts and creativity in schools.

Rosie Millard, the former BBC journalist who is chief executive of the prince’s Children & the Arts charity, said the gathering was the next step in a campaign “to stop the general slide of arts and creativity in schools”.

“The prince is very concerned about it and he wanted to have this day to bring together educationalists, politicians, arts leaders, artists and people to whom this matters,” she said.

But the prince cannot get involved in the politics of the issue and many people in the arts and education sectors see the problem as political. They point to the lack of a compulsory arts subject in the new English baccalaureate and funding cuts to local authorities.

After the event Tom Watson, Labour’s deputy leader and shadow culture secretary, said every child, no matter what their background, should be able to access the arts.

“The government’s ruthless pursuit of the core Ebacc is sidelining vital creative subjects year by year. It will cause us to miss out on potential artists, musicians and actors of the future and it will make the UK’s arts and culture the preserve of the few and even posher than it already is,” he said.

“There is no sense in the course the government has taken. As soon as Labour is in government we will put it right by putting creativity and arts back at the heart of children’s education.”

He said Labour would introduce an arts pupil premium to every primary school; review the Ebacc performance measures to make sure arts were not sidelined; and launch a creative careers advice campaign in schools.

Three government ministers were also at the event, in private roundtable discussions, but did not speak publicly.

The actor Samuel West, chair of the National Campaign for the Arts, attended the event and said “creativity in schools is in freefall”.

“The prime minister has spoken of the need for us to be an imaginative and creative nation in order to deliver a successful Brexit. With arts GCSEs having fallen a fifth in the last decade we might ask where she expects to find the imaginative and creative citizens of the future,” said West.

Among the audience was Andria Zafirakou, who this year was named global teacher of the year and has used her $1m (£770,000) prize money to set up a campaigning charity.

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She said getting the arts into schools was “a battle” and making it a subject in the Ebacc would make a huge difference. “It is not just the students choosing, it is their parents, their community. They will appreciate the fact that these are valued subjects; they are not soft subjects, they are not subjects you should just have as an extracurricular activity.”

Lloyd Webber said cuts to funding for arts in education were “ludicrous” and added: “Arts in education – whatever anybody may like to say – have had their funding reduced and I believe this to be a great, great mistake.”

The issue was about more than just money, he said. “It isn't just about funding. It's not me sitting here bashing the government about funding at a difficult time. It's about other things as well – it's about the attitude of teachers and about them feeling that they want to empower kids to see and enjoy the arts in the widest possible form."