Theresa May's plan to make organ donations automatic by 2020 is doomed to failure, according to new research.
People in England now have to opt in to donate organs but, amid concerns about a shortage of available organs, the government plans to change to an opt-out system, which presumes consent, from 2020.
"We know that now around eight out of 10 people support organ donation but only around a third of people have told their families that they want to donate".
Under the opt-out system, planned to come in from 2020, consent is presumed unless family members decide otherwise.
But a study by Queen Mary University of London suggests it will make no difference at all.
The researchers said this is because the family of the deceased will still get the final say. NHS Blood and Transplant (NHSBT) reported in 2016 that 547 families had vetoed donations since April 2010 despite being informed that their relative had opted in to the register. But if not, this falls to 47 per cent.
Researchers wrote: "When participants know that an individual has registered their decision to donate through some overt signal (i.e. under a mandated choice or a default opt-in system) this is likely perceived as a less ambiguous signal of a preference to donate".
They say the best system is a two-way register, or mandated choice system, whereby people explicitly state either their wish to donate or their objection to doing so.
NHSBT said this resulted in around 1,200 people missing out on potentially life-saving transplants.
In England there have been specific drives encouraging people to tell family members about their wishes surrounding organ donation in the event of their death.
"To help increase actual rates of organ donation, we need more transplant coordinators working with families to help them understand the issues before being faced with a monumental and distressing decision".
"This reduces the ambiguity in trying to infer what someone wanted to do when it comes to donating their organs".
What's the argument for the opt-out system?
And families vetoing organ donation is said to be one of the biggest barriers to donation.
In 2017/18 there were 6,044 people in the United Kingdom waiting for a transplant and 411 patients died while waiting.
More than 5,000 people are now on the transplant waiting list in England.
Commenting on the new study, an NHS Blood and Transplant spokesman said: "This is a decision for the Government and Parliament".
"People who do not register a decision will be deemed to have given consent for donation".