Comedian Simon Brodkin, aka prankster Lee Nelson, hands Prime Minister Theresa May a P45 during her keynote speech to delegates and party members on the last day of the Conservative Party Conference at Manchester Central on October 4, 2017 in Manchester, England | Carl Court/Getty Images Greg Clark: Prank during Theresa May’s speech was ‘serious’ security breach ‘It wasn’t a terribly funny prank,’ business secretary says.

U.K. Business Secretary Greg Clark called for an investigation into how a prankster was able to evade security and get on to the stage during the prime minister's speech to the Conservative Party's annual conference in Manchester Wednesday.

Comedian Simon Brodkin handed Theresa May a mock tax form that British workers receive when they leave a job. Greater Manchester Police said he had legitimate accreditation to access the conference site and stressed that everyone in the conference center had to pass through airport-style security.

Speaking to BBC Radio 4's Today program Clark said, "it wasn't a terribly funny prank. It could have been somebody violent." But he said he admired the prime minister's "guts and grace" as she faced some "pretty difficult and unexpected developments."

Clark said the prankster's actions highlighted a "serious" breach of security, saying the incident "clearly needs to be investigated."

Aside from being interrupted by the prankster, May also struggled with a cough as letters on the set behind her fell off.

“The test of a leader is how you respond when tough times come upon you,” May said, during the speech in an inadvertently apt line.

"People admired the guts that she showed," Clark said.