Food not fit for human consumption could have ended up on dinner tables across the UK, an investigation by the country's food watchdog has found.

The Food Standards Agency (FSA) believes legal loopholes have let unsafe meat pass down the food chain.

It warned on Thursday that a serious threat of disease could have arisen and the threat may still exist.

The government's efforts to clamp-down on unfit meat are not working Andrew George MP

The warning has prompted calls for an immediate review of government policy by the Liberal Democrats.

The FSA has warned that urgent measures need to be taken to prevent the spread of contaminated products.

'Protect consumers'

Its report says some legitimate businesses may have been lax in stamping on food fraud.

This has resulted in "diseased and contaminated food" going on sale and the public being exposed to eating unfit meat.

Liberal Democrat rural affairs spokesman Andrew George MP called for an urgent review of government policy following the FSA report.

"The government's efforts to clamp-down on unfit meat are not working", he said, adding that a review of policy was needed to "protect consumers from unfit food".

He said the FSA should be given the resources to make spot checks for contaminated meat.

"The quality of food handling at all points of the food chain must be guaranteed," he said.

'Tougher penalties'

The BBC's consumer affairs correspondent Nicola Carslaw said the frauds were uncovered through recent criminal investigations.

"The report says it may still be happening," she said.

Contaminated food may still be going on sale, says the FSA

Those pinpointed for particular concern are so-called food brokers who are the "middle men" in the food chain.

They trade in food as a commodity and buy meat in bulk, hold it in storage and then sell it on.

But the FSA warns these middlemen are not always checking the food is fit for human consumption.

It wants tighter controls introduced to block legal loopholes that allow rogue brokers to operate.

It has called for tougher penalties to be imposed against those who put contaminated products into the human food chain.