It is the largest piece to leave Portland intact

They had to study the geology of the quarries to identify a suitable rock, then design an accurate blast to ensure the stone could be removed.

"Obviously managing to find the right-sized piece takes a long time.

"But the most difficult part was lifting the piece on to a road haulage vehicle and taking it off the island," said Shahram Hakimzadeh, operations manager for Hanson Bath and Portland Stone.

Art 'installation'

The stone is being taken to Compton Verney art gallery in Warwickshire where it will form part of an installation by the artist John Frankland.

Portland stone is one of the most important building materials in the country.

It has been quarried since the 12th century, but came into prominence in the middle of the 17th century when it was used for many of London's main buildings, including St Paul's Cathedral.

The Isle of Portland is joined by road to the mainland near Weymouth.