Puzzled customers have been wondering why they keep seeing the Jaffa brand in supermarkets, but then discover that the fruit in question is not grown in Israel.

But a JC investigation has established that Jaffa oranges and grapefruits can be sold by Tesco - but the fruit is not necessarily from Israel.

The brand name Jaffa can be used by Tesco on citrus fruits approved by the Israeli Ministry of Agriculture when the Israeli fruit is out of season.

But other supermarkets may be using the Jaffa name improperly if the fruits are not Israeli.

Customers have spotted red grapefruits labelled as Jaffa which are actually grown in America.

But a Waitrose spokeswoman said: "All our red grapefruits are currently sourced from Israel and have a Jaffa sticker on them."

Mike Lister, citrus project manager at Agrexco, said there was a longstanding agreement between Tesco and the Ministry of Agriculture to use the Jaffa brand name.

He said: "They are very selective about what products can use the Jaffa brand name. It's a really desirable brand and there's a lot of demand for it.

"Tesco wanted to sell the Jaffa brand all year round, but obviously Israeli products are only in season at certain times, so they pay a fee to be able to put the brand name on products, mainly from South America and southern Africa, which are in season at different times."

Tesco is believed to pay the Citrus Marketing Board of Israel NIS 1 million (£168,000) per season for the use of its brand.

He added: "No-one else is licensed to use the Jaffa brand apart from Tesco but it could be that some fruit in other stores is incorrectly labelled or put in the wrong section."