The bus, hired out by packing company Fenmarc, was spotted in Wisbech, Cambridgeshire outside an Asda store distributing potatoes from the Middle East.

BPC chief executive Helen Priestly said: 'I am extremely concerned by this. The circumstances have been full investigated and immediate action is being taken to ensure that it will not happen again.

'The bus is provided as an industry resource to promote British potatoes. For this reason, in addition to its use by the BPC, it is also made available for hire by companies in the UK potato industry to support their own promotions of the UK potato crop. This has been done on many occasions to good effect.

'On this occasion the bus had been hired by the packing company Fenmarc and was being used outside an Asda store. Because it was on private hire, BPC staff were not present. The matter has, of course, been discussed at senior level and Fenmarc has formally apologised for the oversight that led to this local error of judgement.' Enforcement provisions have now been put in place to ensure that such a situation does not occur again.

Chairman David Walker added: 'This is the fourth year that we've been running this campaign and this is the first instance that things have not gone as planned. It's a situation that will not happen again. The whole essence of this campaign is to get everyone throughout the industry to recognise and promote the health aspects of potatoes and it will be good to see the impact of the synergy created from an overall message.'