A Welsh man has expressed his regret after throwing out a hard drive which contained a forgotten cache of 7,500 bitcoins, worth more than £4 million at today’s prices.

James Howells mined the virtual currency on his laptop in 2009 when it was trading for pennies, but today, one Bitcoin is valued at more than $1000. The hard drive containing this sizeable fortune has been tracked to a landfill in Newport, where it lies buried under four feet of rubbish. However, according to experts, the storage device is pretty much impossible to retrieve.

Last month, a Norwegian citizen made the headlines thanks to a forgotten investment he made in Bitcoin in 2009 that years later bought him a flat in central Oslo.

Bitcoins are a decentralised digital currency based on an open-source, peer-to-peer Internet protocol, first introduced in 2009 by an anonymous developer known under the alias ‘Satoshi Nakamoto’. It is not linked to any real money, but traded on various electronic exchanges to establish its price.

The only way to generate new Bitcoins is through mathematically intensive cryptography operations which require a lot of time and computational resources – the process better known as ‘mining’.

According to the Guardian, Howells, now an IT professional, mined his bitcoins on a Dell laptop for a week, but stopped after his girlfriend complained that the machine was running too hot. The laptop was eventually retired and taken apart, but Howells kept the drive with his personal files.

This summer, he was cleaning out his desk, discovered the old drive and put it in the bin, since he couldn’t remember if it contained any important data. Several months later came the horrific realisation that it stored a cryptographic key for 7,500 bitcoins.