Cadbury Schweppes has launched a full investigation into a manufacturing error after the confectionery and drinks company was forced for the second time in two years to recall thousands of chocolate bars.

The company said that a printing problem had led to the omission of nut allergy warning labels from 250g Dairy Milk Double Choc bars.

A spokesman for Cadbury said that the mistake, at the group’s Keynsham plant in Bristol, had been discovered on Thursday and the company was urgently seeking to recall the affected bars, most of which had already been distributed to British supermarkets.

The spokesman said that a full internal investigation was under way as to why the labelling error had gone unnoticed.

The Double Choc bars are produced on a production line that is used to make other products containing nuts, and there is, therefore, a risk of contamination.

The recall is an embarrassing gaffe for Cadbury, which in July was fined £1 million after an incident last year in which some of its chocolate products were found to be at risk of infection with salmonella.

In that incident, the contamination was detected at Cadbury’s Marlbrook plant, near Leominster in Herefordshire. It was linked to a leaking pipe bringing cleaning water into a chocolate crumb plant.

The incident led to the recall of more than a million products and the company was forced to strip down and decontaminate the plant at a cost of at least £30 million.

Cadbury said the latest recall, which affects promotional Dairy Milk Double Choc packs bearing the phrase “win a prize and a half”, was on a relatively small scale compared with last year’s incident.

The spokesman declined to say how much the incident might cost Cadbury, which has advised nut allergy sufferers not to eat the bars and to contact the company for a refund.

Separately, it emerged yesterday that Cadbury had rejected a fresh private equity-backed bid for its American beverages arm worth up to £6.9 billion. The move raised expectations that the group would opt to demerge the unit, the owner of 7Up, Dr Pepper and Snapple.

The approach, from a private equity consortium including Blackstone, Kohlberg Kravis Roberts and Lion Capital, had been rejected by the company’s board because its terms included an unattractive vendor financing proposal.

Cadbury revealed this year that it planned to separate its beverages unit from its core confectionery business, either through a sale or demerger. Last month, unprecedented volatility in the global credit markets forced the group to delay expected plans for a sale to private equity. Since then, Cadbury has insisted that it continues to pursue a dual-track approach and is still considering both a demerger and a sale.

Graham Jones, an analyst for Panmure Gordon, predicted that, by the end of the year, if an acceptable bid was not forthcoming Cadbury would “press the demerger button”.

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