One of David Cameron's closest political friends described Ivan as "a lovely kid" with a "spark".

Ed Vaizey, Tory MP for Wantage, said this morning: "I am still slightly stunned by the news.

"Ivan was a much loved, intensely loved child.

"There is no way David or Samantha ever felt he was a burden or anything. He was a much loved member of the family and they will all be devastated."

Mr Vaizey, who met Ivan on a number of occasions, said: "He was very severely disabled but he was a lovely kid and you could tell there was a spark there.

"I always felt he was part of a family but his disabilities meant there wasn't a lot he could do.

"He was definitely integral to the family."

Mr Vaizey said it would be "incredibly difficult" for Mr Cameron to deal with the loss of his son in the full glare of frontline politics as leader of the opposition.

But, he added: "He is very lucky to have a very supportive family and all his colleagues will rally around and shoulder the burden.

"I think for the next three or four weeks people will understand if he doesn't take the prominent role he has taken so far."