Sainsbury's claims that the rambutan, with its thin, leathery rind covered with soft reddish and yellow tubercles, is the latest craze in exotic fruit.

A promotion to coincide with Comic Relief will see Sainsbury's donate 20p per pack for a red variety sourced in Thailand priced at £1.49. This will be available in 230 of its stores.

Sales have soared by 300 per cent since Sainsbury's increased prominence of the fruit and the store hopes to raise approximately £2,000 for the charity.

Craig Sibbit, Sainsbury's exotic fruit buyer, said: 'Since introducing rambutans in store two and a half weeks ago they have been flying off the shelves. Customers are becoming more interested in exotic fruits and the success of rambutans is proving this.' Sainsbury's is already looking at the potential to sell the fruit for a longer period. There is a small crop in June and July, and a heavier one from November to January.