UK investigating how 500,000 medical letters were misplaced

Britain's National Health Service says it is investigating whether patients were put at risk when half a million pieces of confidential correspondence were mislaid over a five-year period.

The Guardian newspaper reported Monday that blood test results, cancer diagnoses and other papers sent between hospital and family doctors were mistakenly stored in a warehouse by a subcontractor, Shared Business Services.

The newspaper said the error began in 2011 and was discovered in March 2016.

The Department of Health says an investigation is underway but so far there is no evidence patients were harmed.

Opposition politicians are demanding answers from the government. Liberal Democrat leader Tim Farron called the episode "a staggering loss of personal, private data."

SBS is co-owned by Britain's Department of Health and French company Sopra Steria.