The British Government risks bringing an end to the traditional British breakfast if it allows manufacturers to sell jam without enough sugar, a Liberal Democrat MP said.

Tessa Munt said the Department for Environment, Food and Rural Affairs (Defra) should not adopt new rules that will allow jam producers to call their fruit spreads jam even if they are only 50 per cent sugar.

Munt, who is parliamentary private secretary to Vince Cable, said this will mean they will be able to sell a “gloopy sludge” that resembles nothing like the traditional British staple.

She told MPs in a Westminster Hall debate that rules dating back to research in the 1920s meant that jam had to be at least 60 per cent sugar to retain its gel-like quality.

Defra Minister George Eustice said: “One impetus” for the change was an EU “jam directive”. He said it permitted, but did not require, a sugar level lower than 60 per cent to be set.

But Munt said consumers would be left confused if producers were able to sell products labelled as jam when they were only 50 per cent sugar as their consistency would be similar to inferior European fruit spreads that often “tasted like mud”.

She said she was concerned that this debate could herald the end of the British breakfast as “we know it”.

“Reducing permitted sugar levels from 60 per cent to 50 per cent would, in time, destroy the characteristic quality of British jams, jellies and marmalades, and could mislead consumers. We all know what we expect when we go to the supermarket: something of beautiful quality with beautiful colour, with a shelf life of about a year.

“If the total sugar percentage is reduced, the characteristic gel in the consistency of jams, jellies and marmalades will be lost, and the result will be a homogenised, spreadable sludge.

“At a time when public attention is being directed to the content of food, it seems inadvisable to encourage the unnecessary production of food items with additives and artificial flavours,” Munt added.