The Labour peer, who told the Lords he had been threatened with firebombing in the past, said the need for animal research in drugs was probably going to increase.
But pharmaceutical companies were reluctant to put their "heads above the parapet" for fear of reprisals from those opposed to animal testing.
"Animal research in the UK has been very considerably under threat repeatedly for a very long time," Lord Winston said.
"Experimenters like myself who hold licences have found it often very difficult to do research which we regard a medical necessity.
"It is a fact that virtually every drug, every medicine we take, with the exception possibly of aspirin ... is developed as a result of animal research."