The Food Standards Agency has linked a doubling in cases of listeria food poisoning on the increased consumption of chilled food such as pre-packed sandwiches.

Instances of the deadly bug have doubled since 2001 to 400 a year and increased by 20% in the last year alone – a shift the food watchdog blamed on the popularity of chilled, pre-packaged food.

The FSA told the Independent on Sunday the greatest risk lay with pre-prepared food eaten cold such as sandwiches, salads and cooked meats, with consumers reluctant to ditch food that looks safe to the naked eye.

“Although 400 cases each year is still quite small, a lot of them get hospitalised and there is a high proportion of deaths,” said a spokeswoman for the body.

The warning comes with the FSA considering whether to require manufacturers to display use-by information more prominently on food packaging.

"The best before date is about quality but the use by date is about safety," added the spokeswoman said.