News of the iPhone 5S falling short of demand across the UK today resembles almost every big technology release from Apple over the years. But what is the cause of the shortage?

Some would argue that it’s just old-fashioned PR, hoping to drum up excitement and faster-buying when consumers catch whiff of a shortage. A smaller number of 5S devices would make the phone more exclusive, rarer, and that would surely make consumers want to queue for hours for the thing.

Other reasons may be that this is the first time Apple has given their customers a choice on what they’re buying. With the 5C model also released, this could be a way of channeling more buyers into getting the 5C. Either way, customers might leave the store with at least one of the products, so a win-win for Apple.

"This is the first time that Apple has given its customers a choice on phones," said Graeme Neill, deputy editor of Mobile.

"I think this is a way to try and encourage and foster demand for the 5C before it comes out."

It could also be a supply chain problem for Apple, causing the shortages. With advanced technology like the fingerprint scanner and the high-end processor, the company may be having trouble keep up.

However, Apple is expected to post positive sales in China of the 5C, where the phones will also be launched on Friday – the first time the country has got the smartphone on the same day as other markets.

The roll-out of iOS7, the first major reissue of the firm’s mobile operating system since the very first iPhone, has been fast, however news of a security glitch has dampened its reception. Still, around 35% of iPhone handsets are said to be running the software after just one full day of release.

Neill said that despite any adverse effects from low stock, Apple would not be greatly affected longer term.

"They’re an insanely popular brand, people have been queuing at the Regent Street store since Tuesday night.