An opt-out register is unlikely to increase the number of organ donations because family members would be more likely to veto a presumed consent, researchers have said.

The results of a study by Queen Mary University of London suggest that next of kin are more likely to quash a donation if their deceased relative has not given explicit consent.

People in England currently 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.

The government says the move could save as many as 700 lives a year – there were 6,044 people on the waiting list in 2017-18, 411 of whom died – but the study’s authors question this.

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.

Dr Magda Osman, the lead researcher, said: “If you automatically presume consent of the entire nation by putting them into an opt-out system, what you do is you artificially inflate the numbers on the register but it doesn’t necessarily translate into more organ donations.

“Being automatically transferred into the system doesn’t provide a strong signal [to your family members] as to whether you want to donate your organs, so that’s going to exacerbate a problem which already exists.”

Even under the existing opt-in system, many relatives have vetoed organ donation. 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. It said an estimated 1,200 people had missed out on potential life-saving transplants as a result.

People in England currently have to opt in to donate organs but the government wants to change to an opt-out system by 2020. Photograph: BRD Associates

Osman said: “We’ve already got a situation where veto rates are quite high under circumstances where you generally have to indicate consent. Imagine how problematic that’s going to be in circumstances when you can’t really be sure [what the potential donor’s wishes were].”

For the study, published in Journal of Experimental Psychology: Applied on Thursday, 1,294 adults from the US and Europe were presented with fictional scenarios and asked to ascertain the wishes of the potential donor.

The researchers found that regardless of where the participants came from they perceived the donor’s underlying preference to donate as stronger under default opt-in and mandated choice systems (where participants have to express a preference) compared with default opt-out and mandatory donor systems.

Osman said the increase in the number of people on the organ register would also be futile if the necessary infrastructure was not in place. There needed to be the hospitals and staff to carry out transplants as well as nurses to work with families of potential donors, she said. An internal NHSBT document has voiced similar concerns.

Jackie Doyle-Price, minister for heath inequalities, said: “We believe that by making these changes, we will save and transform hundreds of lives every year.

“But organ donation remains a gift ... We know this new system alone will not break down every barrier. We need to address myths and misconceptions around donation, and we will only do this by having informed debate and dialogue, which will be fostered by these proposals.”