If they were children they'd probably be told to grow up, but no one tells billionaires what to do. That's why two of the world's wealthiest men are refusing to back down in their on-going 'mine's bigger than yours' battle to be the owner of the world's largest yacht.

Mega-rich Chelsea Football Club owner Roman Abramovich, who currently owns the world's biggest private superyacht, appears to have been forced to carry out some urgent extensions after Sheikh Mohammed bin Rashid launched a bid to regain the title.

It was only two years ago that Mr Abramovich bought his 557ft-long vessel and stole the crown from the Sheikh 532ft yacht called Dubai.

But, in the wake of rumours that Sheikh Mohammed is having his boat extended to recapture the title, Mr Ambramovich has perhaps not surprisingly booked his own yacht in for a refit in Barcelona harbour.

The mega-yacht is currently moored in the harbour, where it is covered in tarpaulin and scaffolding while the secret work is carried out by Marina Barcelona 92. It is not known exactly what alterations are being done to the yacht, which Mr Abramavich - who will be in Munich tomorrow for the European Cup final - initially bought for around £330 million. The final cost was believed to be £1billion by the time he paid for extra luxury fittings and security measures.   –DM