Cadbury failed to inform food watchdogs about salmonella contamination at one of its factories, despite nine cases of the bacterium being identified over a four-month period.

The confectionery giant admitted to the potential health hazard last Monday, but only, it can be revealed, after pressure from the Food Standards Agency – and then waited until Friday to announce that it was withdrawing a million bars of chocolate.

The company was accused last night of a cover-up and MPs demanded "a full and public explanation" of why it had waited so long to admit to the contamination.

The Food Standards Agency is continuing its investigations and will hold talks with Cadbury this week.