Britain's Parliament stood united in grief on Wednesday after the death of British Opposition leader David Cameron's severely disabled six-year-old son, who battled cerebral palsy and a rare form of epilepsy all his life.

Ivan Cameron, the eldest of Cameron and his wife Samantha's three children, died around 6:30 a.m. local time at St. Mary's hospital in central London after becoming ill overnight, the hospital's chief executive Stephen Smith said.

Out of respect for Ivan and the Camerons, the House of Commons cancelled the weekly prime minister's questions session on Wednesday for the first time since the sudden death of longtime Labour party leader John Smith in 1994.

Prime Minister Gordon Brown, whom polls suggest the 42-year-old Conservative Leader will topple from power when an election is called, led condolences in the Commons, telling MPs that "the death of a child is an unbearable sorrow that no parent should ever have to endure."

"I know the whole country, our thoughts and our prayers are with David, Samantha and their family today," said Brown, who also lost his first child, Jennifer Jane, in 2001 after complications from a premature birth.

'Magical child'

Tory MP William Hague, who stood in for Cameron on Wednesday, told the House that Ivan had brought "joy and love to those around him."

Hague conveyed a message of thanks from the Camerons to the dedicated doctors, nurses and caregivers "who not only did their outmost for their son this morning, but helped him every day from the moment he was born."

George Osborne, the Conservative shadow chancellor and a close friend of the Camerons, told the BBC the couple are "devastated" by the loss.

Cameron had often spoken publicly about his son's disability, and how his family's experience with Ivan helped shape him to become a passionate supporter of the state-funded National Health Service.

In a 2006 interview with the BBC, Cameron said learning that his son was severely disabled had hit him "almost like mourning."

"You're mourning the gap between your expectation and what has happened," he said.

He also described Ivan as "a magical child with a magical smile that can make me feel like the happiest father in the world."

"We adore him in ways that you will never love anybody else, because you feel so protective," he said in a 2007 speech.

The Queen has also sent a private message of sympathy to the Camerons, Buckingham Palace said.

With files from the Associated Press