LONDON (Reuters) - British retailer Marks & Spencer warned on Friday its popular Percy Pig sweets could be hit by tariffs if it re-exports the product to European Union countries, including Ireland. Chief Executive Steve Rowe said the pink sweets, along with about a third of the products in M&S’s food business, are subject to very complex “rules of origin” regulations that form part of Britain’s trade deal with the EU struck on Christmas Eve. The rules relate to the composition of individual products and how much of it has been altered in the United Kingdom. Any product that is manufactured in Europe, imported into the UK and then re-distributed to EU countries faces a tariff. “The best example I can give you of that is Percy Pig,” Rowe told reporters, as M&S updated on Christmas trading. “Percy Pig is actually manufactured in Germany. If it comes to the UK and we then send it to Ireland, in theory it would have some tax on it,” he said. M&S warned on Friday the tariffs issue would significantly impact its businesses in Ireland, the Czech Republic and its franchise business in France. It said it is working to mitigate the problem.