The world’s most expensive privately-owned yacht is being built in Genoa, Italy, the Sunday Telegraph reports. Known only as ‘Hull 6154’, the yacht measures 438ft, with seven decks, two helicopter pads and storage space for a submarine, and boasts a record-breaking price tag of £140 million. Its 60-strong crew will entertain guests in 15 state rooms fitted with the latest entertainment systems, gold and marble bathroom fittings and Jacuzzis. And if guests grow tired of the onboard delights, they can explore further afield using one of the yacht’s five jet-skis or two speed boats.

The owner of the yacht, due for completion in 2010, is as yet unknown, but sources say that it is a Russian billionaire. However, Roman Abramovich, the Russian owner of Chelsea Football club who already has four yachts to his name, has been ruled out. Abramovich’s yachts include the 335ft, £72 million Pelorus, and he recently announced that he was commissioning a fifth vessel called The Eclipse, priced at over £100 million. Currently under construction in Hamburg, it’s security is said to include bullet-proof glass and a missile detection system.