One in six mobile phones is contaminated with faecal matter, according to new research.
Experts said the most likely reason for the potentially harmful bacteria festering on so many gadgets was people failing to wash their hands properly with soap after going to the toilet.
The survey also revealed a tendency for people to lie about their hygiene habits.
Although 95pc of people said they washed their hands with soap where possible, 92pc of phones and 82pc of hands had bacteria on them.
Worryingly, 16pc of hands and 16pc of phones were found to harbour E.coli -- bacteria of a faecal origin.
Harmful E.coli (Escherichia coli) is associated with stomach upsets and has been implicated in serious cases of food poisoning such as the fatal O157 outbreak in Germany in June.
Dr Val Curtis, from the London School of Hygiene & Tropical Medicine, said: "This study provides more evidence that some people still don't wash their hands properly, especially after going to the toilet.
"I hope the thought of having E.coli on their hands and phones encourages them to take more care in the bathroom -- washing your hands with soap is such a simple thing to do but there is no doubt it saves lives."
Researchers travelled to 12 cities in Britain and took 390 samples from mobile phones and hands which were analysed in the lab to find out the type and number of germs lurking there. Participants were also asked a series of questions about their hand washing.
The largest proportion of contaminated phones was in Birmingham (41pc), while Londoners were caught with the highest proportion of E.coli present on hands (28pc).
However, actual levels of bacteria increased the further north the scientists went -- the dirtiest city being Glasgow. There, average bacterial levels on phones and hands were found to be nine times higher than in Brighton, reinforcing a north/south divide.
The scientists also found those who had bacteria on their hands were three times as likely to have bacteria on their phone.
The findings were released ahead of the annual Global Handwashing Day on Saturday.
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