Almost a third of men and many women do not wash their hands after going to the toilet vastly increasing the risk of food poisoning, says a survey.

Many are transferring germs straight from toilet to plate because they also do not wash their hands before preparing food.

To launch National Food Safety Week on Monday, the Food and Drink Federation stressed that even healthy guts can contain potentially harmful bacteria.

They illustrated the danger by releasing pictures which revealed just how many bugs are carried by unwashed hands.

The light patches are germs carried on the hands

People were asked to make a impression on special agar jelly with an unwashed hand.

When ultraviolet light was used to compare the amount of bacteria growing within the handprint with those from a washed hand, the difference was visibly dramatic.

Estimates suggest as many as 4.5 million people suffered from food poisoning in the UK last year - although fewer than 100,000 cases were reported to the authorities.

The main culprits were salmonella, campylobacter and e.coli.

A quarter of men

The survey of more than 2,000 people found that a quarter of men, and 17% of women did not always wash their hands before preparing food.

It found 31% of men and 17% of women confessed to not washing hands after going to the toilet - many of these believed the toilet was clean, or that they were only coming into contact with their family's germs.

One in five said they did not bother because their hands looked clean.

Professor John Krebs, chairman of the Food Standards Agency, said: "Handling food with dirty hands is asking for trouble. Food poisoning is still a big problem in the UK and the simple step of washing our hands will help reduce risks and clean up our act."

Handling food with dirty hands is asking for trouble Professor John Krebs, Food Standards Agency

Other findings of the survey were disturbing - for example, only 37% of people knew the correct working temperature of a fridge.

Forty-two per cent did not always wash their hands after playing with pets, and more than half did not wash before eating food.

Professor Hugh Pennington, a microbiology expert from the University of Aberdeen, said: "There will be those who accuse us of being patronising by focusing on something as basic as handwashing.

"I say to them: 'The next time you meet someone and shake their hand - there's a one in five chance that they are one of those who do not always wash their hands after going to the toilet'."