Thames Water brought the case after finding fat levels of up to three times the limit for trade effluent in the sewers outside two of Noon’s plants.
Noon sells pre-prepared meals under its own name and those of several leading supermarkets. The problems occurred at its plants in Southall, Middlesex, between October 2006 and August 2007.
Appearing before Uxbridge magistrates on 14 January, the firm pleaded guilty to 13 charges brought under section 121(5) of the Water Industry Act 1991. It was fined £3,000 for each offence and £9,599 in costs.
"Prosecutions of this sort are rare and only used as a last resort when a trader fails to respond to correspondence, meetings and repeated warnings," said Sarah McMath, asset performance manager at Thames.
"Fat, oil and grease causes a huge problem for us, as they harden and block the sewers, causing flooding to homes and properties. Last year, we cleared 70,000 sewer blockages, of which we estimate 60 per cent were caused by fat, oil and grease being poured down drains."