A member of staff at Crow Hill Farm in Ringwood, Hants, yesterday found a section of the perimeter fence cut and 40 cages opened. The Animal Liberation Front claimed responsibility for the first raid, which it is feared could devastate the local ecology. It is not known whether the latest break-in is the work of the ALF or another group.

A spokesman for Hampshire Police said: "It really is hard to believe that someone could be so irresponsible. The earlier attack took up a great deal of police resources. Now we are back to square one."

The Ministry of Agriculture said its staff, who were trying to trap all the mink released in the first raid, now faced having to capture many of the same animals a second time.