A play that delves into the role of artists in history and politics was given an R18 rating by the Media Development Authority (MDA) for "mature content" a day before its opening night - the very day the final script was submitted.

Those under 18, as well as schools which have purchased tickets for their students, will receive refunds.

Manifesto, a collaboration between theatre stalwarts The Necessary Stage and Drama Box, opens tonight, and comprises four fictional stories that explore the relationship between artists and the state over seven decades.

In the first, a young painter is forced to leave his family and his art due to the political tumult of the 1960s. The second follows writers detained by the Internal Security Bureau in 1987, while the third sees present-day artists trying to find a space to practise their art, free from the intervention of the state.

The final story takes place in 2024 and tells the tale of a theatre company discovering its hidden past.

For such a complex play, which also features a cast of actors of different ethnicities, from veterans such as Sani Hussin to younger performers such as Ellison Tan, changes had to be made to the script time and again.

The Necessary Stage's general manager Ms Melissa Lim says: "We are very grateful to MDA for accommodating our changes for the script and multimedia.

"Given that Manifesto is a devised and interdisciplinary work, tweaks and amendments are inevitable and MDA has been liaising with us through all the changes made."

The company had been alerted of the possible R18 rating a few days ago by the MDA, but only received confirmation yesterday.

Initially, 43 tickets had been set aside for school bookings. These have since been released for sale.

But since the R18 rating was announced, there have been more returns, she says, including those from schools that had purchased tickets for students on their own.

As of 1.30pm yesterday, an additional 40 tickets were being refunded, most of them for the first show tonight. Those under 18 who have purchased tickets and would like a refund can e-mail admin@ necessary.org.

An MDA spokesman says the final script for Manifesto was submitted yesterday - after the Feb 24 deadline - and its original application had also been submitted "less than the required two months before the play". The production, he adds, was given an R18 rating with the consumer advice "mature content", "as it deals with socio-political issues that are more appropriate for a mature audience".

According to its Arts Entertainment Classification Code, a show can be classified R18 if it contains contentious racial or religious issues, explicit references to issues or lifestyles contrary to "prevailing social norms", violence, nudity, strong sexual content or the use of strong expletives.

The Necessary Stage's founder and artistic director Alvin Tan, who is co-directing the play with Drama Box artistic director Kok Heng Leun, says: "I didn't expect an R18 rating because I believe our young today should have the opportunity to engage with challenging art, so that was why we had opened ticket sales to students."