The confectionery giant Mars has also dropped the slogan "A Mars a day helps you work, rest and play" from wrappers and replaced it with "Now ... there is only one Mars".
A Mars spokesman said last night that the secret recipe had been modified to make it "even smoother" but he could give no details. The new bars have just started to appear in the shops.
"We have modified the recipe," he said. "And some of the new bars have starting arriving in shops before we could make the official announcement. We think people will like the new version."
New bars list ingredients in a different way although the basic mix of milk chocolate, glucose syrup and sugar remains. The weight, 65g, is also the same and the price, at least in central London, stays at 30p although it will vary throughout the country. New wrappers carry the same Mars slogan, but are now highlighted with yellow.
The change comes as Rowntree's rival Kit-Kat bar establishes an increasing lead over Mars at the top of the UK chocolate table. Figures produced earlier this year by analysts showed that Kit-Kat had 17.3 per cent of the market, compared with Mars's 11.7 per cent. In 1993, Mars was just 1.4 per cent behind with 16 per cent. But the two brands are still way ahead of the third-placed bar,Twix, which had 8.6 per cent.
Market watchers say changing attitudes to health and fitness had damaged Mars's sales figures with Kit-Kat and Twix being seen as lighter snacks.
Mars was born 63 years ago in a one-room factory at Slough, Berkshire. It was launched by American entrepreneur Forrest Mars, whose father, Frank, had launched Milky Way in the United States in the 1920s.
The Slough factory now turns out about three million Mars bars a day.
Mars said the recipe was last modified about three years ago. The make- up of the Milky Way was altered at about the same time to take account of changing tastes.Reuse content