A proposed law seeking to give doctors legal protection to use innovative treatments on patients when other options had been exhausted has been vetoed by the Liberal Democrats.
Lib Dem health minister Norman Lamb said he wanted to avoid "the risk of unintended consequences" of Lord Saatchi's Medical Innovation Bill, which went unopposed in a third reading by the House of Lords and was set to go to the Commons.
But the Conservative peer said he was "in a state of shock" over the revelation, telling the Sunday Telegraph it was a "death sentence" for patients with diseases such as cancer.
Lord Saatchi has been campaigning for a change in the law since his wife, novelist Josephine Hart, died from a form of ovarian cancer in 2011.
Under the proposed legislation, a doctor must obtain the views of one or more appropriately qualified doctors on the proposed innovatory treatment.
Writing on the Telegraph's website Mr Lamb MP said the Lib Dems had consulted patient organisations, research charities, legal bodies, royal colleges and medical unions, which each had concerns it could be a risk to patient safety.
"I have enormous sympathy for all those who have been through the awful experience of not being offered treatment which they believe might offer a chance of survival or of improving their condition," he wrote.
"But getting the law right in this area is incredibly important. We have to avoid the risk of unintended consequences.
"I am not interested in pushing this into the long grass. It should be given priority, but we must get it right."
Mr Lamb added the proposal should be reviewed by an "eminent person" before potential draft legislation could go through Parliament later this year.
But Lord Saatchi told the Sunday paper: "By killing the Bill they have killed the hopes of thousands of cancer patients. It is as simple as that. Nick Clegg has handed down a death sentence to cancer patients. It is an extraordinary turn of events.
"This is a grotesque insult to the House of Lords. The Liberal Democrats are saying that the House of Commons will never debate this Bill which has been sent to it and passed by the House of Lords."