South West Water is confident there is not a sewage problem at Instow

Teignmouth, Torre Abbey in Torbay, and Capstone at Ilfracombe failed the guideline standard.

But Instow failed to meet the lowest minimum EU standard during weekly tests between May and July, carried out by the Marine Conservation Society (MCS).

Tests were taken at 40 other beaches in Devon and 78 beaches in Cornwall, none of which failed.

Brushing it under the carpet doesn't do anyone any good Instow holidaymaker

Several factors could have affected the quality of the water, including pollution, heavy rainfall or animal fouling and the MCS said investigations must be carried out at Instow to discover the cause.

South West Water, which has recently invested �13m in a new treatment plant in the area, said it was confident the failure was not attributable to sewage, although it said it would carry out extra checks.

This year, 26 beaches in Devon and Cornwall were awarded the prestigious Blue Flags and 65 South West beaches were given the Seaside Flag awards.

But the MCS report is a blow for the areas which are popular with holidaymakers and day-trippers.

The father of a family from Coventry staying in Instow who did not want to be named said: "People need to have a choice, so if there's a problem here they can go elsewhere.

"Brushing it under the carpet doesn't do anyone any good."

His wife said her main concern was for their children.

"Obviously they're always in the water and the last thing you want on holiday is poorly tummies and illnesses."

More than 100 beaches in Devon, Cornwall, Somerset and Dorset passed the main EU levels.