The Royal Mint is offering "serious investors" with around £25,000 to spare the chance to buy a fine gold bar weighing a hefty one kilogram.

The new gold bars have been produced to mark the first anniversary of a bullion trading website launched by the Mint last year, which aims to make it easier for people to invest in gold at "relatively affordable" prices.

The royalmintbullion.com website has attracted more than 12,000 customers from across the world since it launched in September 2014, from countries including the United States, India, China and Canada.

Up until now, the weight of the bullion bars on offer has ranged from one gram to 100 grams. Investors looking just to dip a toe in the water can also buy silver from the website at prices starting at around £20.

At the other end of the spectrum, the Royal Mint said that its new Kilo Gold Cast Bar will be a "high-value purchase opportunity for serious investors and those who wish to own and trade larger amounts of gold".

The Mint has not given a price for the new bar, as the cost of precious metal changes constantly and the trading website gives live updates of gold and silver prices to reflect this.

But based on current gold prices, the bar, which measures 53mm by 118mm and is 8mm thick, could be worth somewhere in the region of £24,000 to £25,000.

The kilo bar, like all the Royal Mint's bullion bars, bears the Mint's RMR (Royal Mint Refinery) branding.

When it launched the bullion trading website in 2014, the Royal Mint pointed to research by the World Gold Council suggesting that there is potentially £4 billion worth of untapped demand for gold investment within the UK alone.

The Mint said it has seen a 57% increase in bullion sales since launching the website.

Chris Howard, the Royal Mint's director of bullion, said the Mint's 1,000-year history means that it is recognised around the world as a reliable authority on precious metals.

He said: "As royalmintbullion.com passes its first anniversary and begins to mature, we wanted our offering to reflect this and felt the Kilo Gold Cast Bar adds depth to our range and will appeal to the serious investor."

Customers can have the bullion delivered direct to their home by an insured postal service or store their gold in "the vault" - the Royal Mint's on-site precious storage facility which is protected around the clock by the Ministry of Defence.

Storage fees are charged at 1% of the market value of the gold being held, plus VAT, per year.

Customers who are storing bullion in the Royal Mint's vault can also have the option of selling their gold back to the Mint. If the Mint accepts a "buy back" request from a customer, it will give them a quote based on current precious metal prices.