Tory MP James Brokenshire has resigned as security minister, telling Boris Johnson that his recovery from lung cancer treatment is “taking longer than anticipated”.

Brokenshire wrote to the prime minister thanking him for his support as he undergoes treatment following the “frustrating recurrence of my lung cancer”.

“My recovery from treatment and return to full duties is, however, taking longer than anticipated,” he said.

“Given my responsibilities to the public, the government and to parliament, I have therefore concluded that it is best that I stand down from my ministerial role and focus on restoring my health.”

Johnson offered his full support to Brokenshire on his decision to focus on his recovery and wished him a “speedy return to full health”.

“I understand entirely your need to step down from your role but look forward to welcoming you back as soon as possible,” the prime minister wrote.