Animal rights groups threaten to sabotage Lord Rogers and Renzo Piano's sheep herding across the Millennium Bridge.

Animal rights groups have threatened to sabotage Lord Rogers and Renzo Piano's sheep herding through the streets of London tomorrow.

Organisers of the event have received threatening phone calls this week from furious animal rights activists, claiming they will hijack the event on Saturday morning if it is not called off.

They claim the sheep drive, which will see 60 sheep herded from Borough Market to Smithfield Market across Millennium Bridge, will upset the animals and should be cancelled.

The source told Building the event would definitely go ahead. The source said: "The sheep are being extremely well looked after. We are following UK and European regulations for the transportation of animals, we have consulted with the RSPCA and there will be a vet to accompany the journey. What more could they want?"

Lord Foster had originally agreed to drive the sheep over Millennium Bridge but pulled out at the last minute, saying he had to go to a meeting in New York.

Rogers and Piano agreed on Tuesday they would lead the flock.