Experts have admitted they are clueless as to why Welsh people consume much less salt than those living in England and Scotland.

This week the FSA published its urinary sodium survey, conducted at the tail end of 2005, which showed weighted average daily salt consumption across Britain had fallen to 9g from 9.5g in 2001. But while average consumption was 9g in England and 9.1g in Scotland, in Wales it was just 8.1g.

The FSA admitted it had considered several theories for the difference - including one that Welsh people lived further away from supermarkets than the Scots and English, and therefore ate fewer ready meals. But none had stood up under scrutiny.

"There is currently no evidence of differences that would explain the different salt intakes in Wales and the rest of Britain," said an FSA spokeswoman. "We will therefore be following up this work with a further urinary sodium survey in 2007/08 to track progress.

"The new National Diet and Nutrition Survey rolling programme will also provide urinary sodium data. It will also collect information on food consumption patterns and discretionary salt use, allowing us to investigate differences in salt intakes in detail."

The FSA has set a target of cutting salt consumption to an average of 6g per person per day by 2010. It said the latest survey had taken place before a huge wave of reformulations had taken place, in which salt levels in hundreds of lines were cut.

The FSA's latest wave of salt-themed advertising began this week. The Full of It campaign, fronted by comedienne Jenny Eclair, aims to get people checking how much salt is in products, and stresses that 75% of the salt we eat is already in the food we buy.