SABMiller has accelerated the handover of the company to its new chief executive following the news that boss Graham Mackay has been diagnosed with a brain tumour.

Chief operating officer Alan Clark, who had been due to take over in July after a year’s transition, will take over the top spot with immediate effect.

Mackay had been due to take up the role of non-exec chairman, but the company said that it will keep his position under review while he undergoes a course of treatment, after confirming that he had surgery yesterday.

In the meantime, deputy chairman John Manser will become acting chairman.

Graham Mackay of SAB Miller

Graham Mackay of SAB Miller has stepped down due to ill health.

Manser wished Mackay a speedy recovery and said the board’s thoughts were with the Mackay family. He said the succession transition was already in its final stages and that the board was confident that the business would continue to grow.

“SABMiller has a strong management team, with considerable depth of talent, which I have seen for myself during my 12 years on the board, and we are confident that under Alan Clark’s leadership the management team will continue to grow our business and deliver value to shareholders,” he said.

In a note to staff, Mackay thanked them for their support and said that the group was in “excellent hands”.