Back in 2010, an early user of the online currency Bitcoin paid 10,000 Bitcoin for two pizzas from the Papa John's chain.

Today, a Bradford estate agent has put a two-bedroomed terraced house in Leeds on the market for just 10 Bitcoin - now reckoned to be worth £60,000 and rising faster than any other world currency.

But what is Bitcoin and how does it work?

Bitcoin is a “cryptocurrency” - a type of currency that exists only in the digital world.

Transactions take place between users directly, without an intermediary.

These transactions are verified by network nodes - essentially, the computers of other Bitcoin users - and recorded in a public ledger called a blockchain that is distributed across the network of Bitcoin users - so there is no 'master copy' and no equivalent of a central bank in charge.

Those who operate using Bitcoin are able to transfer funds almost immediately, and there is no middle man or major tacked on fees associated with the transactions.

They register as a user, and can transfer money from real world accounts to digital Bitcoin accounts.

New Bitcoins can also be created, or 'mined', by using a powerful computer setup to help 'verify' the blockchain - that is, make sure the ledger tallies up with transactions made.

It has been compared to the gold markets, or the stock market, as the value of each Bitcoin can rise or drop depending on market conditions.
Some refer to Bitcoin as 'digital gold'. 

Recent studies have found that there are between 2.9 million and 5.8 million unique users of Bitcoin.

Bitcoin has been met with suspicion from some corners, with some experts calling it a poor investment and others pointing out how the value of Bitcoin has increased rapidly in recent months, and is currently at its highest level.

Large-scale Bitcoin mining operations, particularly in the developing world, have also been criticised for their effect on the environment because of the massive amounts of electricity they use.