The British Museum faces growing pressure to return the Parthenon Marbles, according to a poll conducted by research firm Mori in the run-up to the opening of the Acropolis Museum in Athens.

The survey of 2,109 people found 47 per cent in favour of their return -up 7 per cent since the last Mori poll in 2002. Only 10 per cent wanted to keep the artefacts, compared with 16 per cent previously. Within this sample, half of those questioned were already familiar with the debate, and 69 per cent of these were in favour of the marbles' return.

The results will put pressure on the British Museum, which faces a public relations battle when the Athens museum opens next year.

Greece will argue that the British Museum can no longer justify keeping the Parthenon Marbles, especially now it has space to house all the artefacts under one roof.

The Acropolis Museum will include a gallery which can display the full length of the Parthenon Frieze.

Eleni Cubitt, secretary of the British Committee for the Reunification of the Parthenon Marbles, said the Mori poll and the opening of the Acropolis Museum would provide a springboard for a resurgent campaign.

She said Greece accepted that the British Museum was the legal owner of the marbles, but added that the issue was an ethical, rather than legal, argument.

A British Museum spokeswoman said: "The issues surrounding the Parthenon sculptures are complex. The British Museum believes that the sculptures in our collection are an integral part of the overview of world civilisations that the museum exists to present. Our visitor surveys indicate overwhelming support for the concept of a world collection."