These findings are revealed in a Panorama Special: How Safe is Your Hospital? to be screened on Sunday evening.
The programme has also carried out a Freedom of Information survey of every acute trust and health board in the UK, to which 83% of trusts replied.
It was announced this week that C. difficile infections in England fell by 8% between October and December 2007.
However, Panorama has learned the way cases are counted has changed, and experts calculate that the real figure is actually between 16 and 35% higher than this - making a substantial increase on the last quarter.
In Scotland too the number of cases went up by 10%, and in Northern Ireland there was a hefty rise of almost 36%.
Comparable figures for Wales aren't out yet. The UK as a whole remains bottom of the world league.
Carol and Jackie said people were dying around their mother all the time
Professor Richard James, who runs a leading centre in Nottingham University to investigate hospital infections, said: "The figures for c.difficile show that more than 50% of hospital trusts in the UK have a rate of infection that's more than 10 times that of any other country.
"If you look at the over 65s, which are the group where there are more deaths, then we have more cases there, and therefore more deaths in that age-group than any country in the world by a factor of 10."
His remarks are based on a draft report to the Department of Health from the influential steering group on healthcare-associated infection, which is currently out for consultation.
While the figures are based on English acute NHS trusts, Professor James said they were relevant to the whole of the UK.
We actually joked that they might have a deal with the undertaker because we actually saw so many bodies going out
Professor Brendan Wren, of the London School of Hygiene and Tropical Medicine, told Panorama: "The deaths of 6,500 people a year is the equivalent of one person dying every hour in our hospitals."
Of the 170 trusts which replied to Panorama's Freedom of Information survey, a majority of 95 had bed occupancy rates of more than 85%.
Professor James said: "Experts would say if you go above 85% bed occupancy rates then that is not conducive to good control of infection measures."
The survey also reveals that 94% of hospitals now have alcohol hand gels outside their infection wards - which is effective for MRSA.
But alcohol hand gels don't work against C. difficile.
To show what happens when hospitals get infection control wrong, Panorama was given unprecedented access to the Maidstone and Tunbridge Wells trust in Kent, where around 90 patients died in two outbreaks of C. difficile in 2005-6, with more than 1,100 people infected.
The trust is now under new management.
One of the patients who died in the second outbreak there was 83-year-old Mary Hirst, who was admitted to Maidstone Hospital on 8 April after a fall.
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