Samsung's stock issues with the new Galaxy S4 flagship are apparently far from over, as UK networks are struggling to meet pre-order demand.

Networks in the UK are reportedly failing to find enough stock to fulfill Samsung Galaxy S4 pre-orders. While Galaxy S4 shortage issues are no longer a surprise, supplies are now so low that British operators actually found themselves unable to send the smartphone to all pre-order customers, even if they paid weeks ago for the device.

"We have dispatched phones to customers who pre-ordered, although we still don't have enough to cover all pre-orders," Vodafone told CNET in a statement. "We're working with Samsung to get more devices as soon as possible."

UK carrier Three seems to be facing the same difficulties, with moderators on the pre-order page telling a similar story.

"We're sorry you didn't receive your phone as planned," moderator Johanna writes in reply to one pre-order customer. "Our stores had minimal stock to fulfil some pre-orders but sadly not all. The stock was split between stores, online and telesales. We are getting more stock in this week and hope to fulfil all pre-orders by Friday [May 3]."

Meanwhile, O2 appears less affected by the shortage woes, but reckons that its stock of the Samsung Galaxy S4 is "still limited."

While many wonder how Samsung came to such issues, it's fairly common for handsets in high demand to sell out quickly after launch. One theory making the rounds is that manufacturers sometimes deliberately cut stock numbers to tout their devices as "sell-out" hits, but that's most likely not the case here. The fact that stock is not even sufficient to fulfill all pre-orders on time suggests that Samsung underestimated the demand for its newest flagship and is now unable to deliver as many units as networks expected.

When news of the supply shortage first surfaced last week, Samsung said the stock issues were due to "overwhelming global demand." The company said it is working hard to ensure that Galaxy S4 pre-orders and sales across all channels are "fulfilled as soon as possible."

Customers who pre-ordered the Samsung Galaxy S4 weeks ago but have yet to receive it are becoming increasingly anxious, flooding networks' forums and support pages to complain about the delay.