Gordon Brown's eyesight is causing concern among aides

The Prime Minister's close friends have revealed that he can only see extremely large print and has needed guidance at public events. There were suggestions that if Mr Brown falls or bumps into something his damaged retina could fail and he would go blind completely.

Mr Brown, who was left blind in one eye after a rugby accident at the age of 16, addressed the problems in an interview when he admitted that he is suffering increasing problems with the other eye and recently had to have a cataract removed.

Appearing stoical, he said he had "enough" sight but admitted: "It does mean when you're speaking to an audience you automatically tend to correct [which direction to look in] so you've got to be careful. If you're reading something you have to look slightly to the side."

Damian McBride, Mr Brown's chief spin doctor until the reshuffle, is quoted as telling the interviewer: 'His sight isn't very good.'

Insiders also revealed that Mr Brown's memos are in huge print and triple spaced while his own handwriting is getting larger. One senior official said: "If I want him to reply to an email, I always make sure it's in at least 36 point." That is five times as large as standard print size.

There is mounting anecdotal evidence that Mr Brown is battling a serious disability. As this newspaper revealed last month, the Prime Minister has been daubing black ink all over the Commons' dispatch box during Prime Ministers' Questions.

Aides have now also revealed that at the Labour spring conference the Prime Minister took a wrong turn off the stage and failed to find the exit.

When he was about to meet a line-up of war veterans recently, the former minister John Reid had to be moved out of the way because Gordon "would have confused him with a veteran", according to one aide.

"You can't understand Gordon if you don't understand his fear that he could go blind at any moment,' one friend said. "In public Gordon puts on a heroic performance, but there is always a cost."

The revelations may be an attempt by Number Ten to explain to the public why the Prime Minister appears to stare blankly and awkwardly sometimes. The apparently frozen expression on his face and forced looking smile has been one of his biggest disadvantages in connecting with the public.

There were also suggestions last night that Mr Brown's legendary temper was down to his frustration at his own limitations. "The anger is actually very much about him," one friend was quoted as saying.