The latest incarnation of Apple's iPhone has already sold around 1.5 million units, according to statistics by US investment banking firm Piper Jaffray, making it the most successful mobile phone launch in history.

In the States the firm also found, after questioning iPhone buyers in several cities, that a whopping 77% of those queuing for the new iPhone were upgrading from an older version of Apple's ubiquitous smartphone.

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In the UK, retailers in London including Carphone Warehouse, Phones4U, Orange and Vodafone have been running out of stock due to the demand, according to V3.co.uk.

Retailers which began selling the iPhone 4 on Thursday were warning in advance that stock would be low for the UK launch of the iPhone, with O2 going as far as to restrict its stock of iPhones to those who were already O2 subscribers.

Retailers claim they will be receiving new stock next week, although only of the black iPhone 4 model, with the white model hitting the UK sometime in July.