BUYERS of this wartime motorbike are guaranteed to have a blast - because it comes with a its own machine gun mounted on it.

The First World War was first privately owned by a man from Dorchester and is expected to fetch around £30,000 when it goes under the hammer.

It was built in Britain in 1917 on order for the Russian army, and kitted out with the most cutting edge weaponry including a portable Vickers anti-aircraft machine gun operated from a sidecar.

However, following the Russian Revolution that same year they pulled out of the conflict before they could take delivery of the machines and they were left at British ports.

After the war ended in 1918 the British government decided to hold an auction to get rid of the consignment of 250 brand new bikes which had been made by London marque Matchless.

They were sold off for around £64 each - the equivalent of around £5,000 in today's money.

Registration papers show the bike's first owner was Edward Foster from Dorchester in Dorset but little is known of its post-war history from then until it was bought by WWI enthusiast Chris Roberts in 1998.

The bike was in such good condition because it is thought it had been stored indoors for at least 60 years.

Mr Roberts, a member of the Great War Society, set about restoring the bike to its original wartime specification which included adding a Vickers machine gun.

The gun, which is deactivated but cockable, can be fitted to three separate mounts on the bike allowing the gunner to fire in all directions.

It has since been displayed at numerous First World War re-enactments including at the Bovington Tank Museum.

The motorbike is one of only three First World War machine-gun bikes in the country - the other two are in museums - and is the only surviving one made by Matchless.

It is tipped to fetch £30,000 when it goes under the hammer at London auctioneers Bonhams.

James Stensel, from Bonhams' motoring department, said: "This bike has a particularly interesting history - a batch of 250 of these bikes was manufactured in Britain in 1917 for the Russian military, our allies, but they then dropped out of the war and the bikes were no longer needed.

"Instead they were auctioned off and bought by private collectors for civilian use.

"This example didn't see military action. It would have been at a British port ready for dispatch to the Russian Army but when they cancelled the order it was sold off.

"When the machines were readied for dispatch they would have consisted just of the motorcycle and the side car. The Russians would have then added their own military hardware.

"The Vickers machine gun on this bike is a later edition but is just like the ones that would have been mounted on these bikes in the war.

"It's got an anti-aircraft machine-gun mount allowing the gunner to shoot in any direction. The machine gun is also detachable and fully telescopic so if you wanted you could take it off the bike and use it separately.

"The outfit can seat three people - one on the main saddle, another on a pillion saddle and a third in the sidecar.

"These would have been the ultimate motorbike attack vehicles of their day.

"They're incredibly rare now - you only ever see them in museums and never in auctions.

"There are only three known to exist in the UK and this is the only one made by Matchless.

"Not only is it a part of Russian military history but of ours as well. In 1917 Britain was producing the most advanced motorcycles in the world and this no exception."

The auction will be held on Saturday.

The bike's owner Chris Roberts, 65, said he hopes it will be bought by a British museum.

Mr Roberts, from Gloucestershire, said: "I joined the Great War Society in 1997 and my role in reenactments was that of a dispatch rider.

"I've been a fan of motorbikes since I was 15 so when in 1998 the opportunity to buy this Matchless motorbike came up I couldn't refuse.

"It must have been dry stored for many years because it was in such good condition. Even now, most of the bike is original.

"A lot of time and effort has gone into this bike but I have had a great deal of pleasure taking round the country and showing it to people.

"My hope is that it will be bought by a British museum where the public can enjoy it."