This article was written by Steven Morris, for guardian.co.uk on Monday 18th June 2012 15.21 UTC

Details of the first organ donation scheme in the UK that puts the onus on people to opt out if they do not wish to take part have been published. Under the Welsh government’s scheme, people will be given the chance either to opt in formally and agree to become a donor when they become adults at 18 or opt out by placing their name on a register.

However, those over the age of 18 who do neither will be deemed to have made a positive decision to donate organs and tissue for transplantation.

Church leaders have expressed concern at the plans, which are to come into force in 2015. In a joint statement, the bishops of the Church in Wales said organ donation should be freely given, not assumed.

But the church is pleased that, under the plans, the thoughts, feelings and beliefs of the donor’s family will be crucial. If a person does not opt in or out, their families are not legally required to give their approval. But the Welsh government said that in practice a donation will not happen without a family’s “assistance”.

A spokesperson said: “In cases where a person has neither opted in nor opted out, family members are not required to give their consent to the donation itself because the deceased’s consent will have been deemed to have been given already.

“However, it is important to stress the issue of donation will be approached sensitively and, as now, families will still be involved in the process, which cannot go ahead without their assistance.”

A government spokesperson explained that when a donation went ahead, doctors always spoke to family members about matters such as the lifestyle of the deceased. If they chose not to give this information because they did not approve of the donation, the process would be halted. Effectively, this gives families some wiggle room.

Lesley Griffiths, the Welsh health minister, who launched the draft human transplantation (Wales) bill at a sports stadium in Cardiff, said: “We are seeking a change in the law to increase the number of organ and tissue donors and to save lives.

“One donor can improve or save the lives of up to nine other people by donating their organs, and many more through the donation of their tissues.

“Wales has seen a 49% increase in donation rates since 2008, which is a huge achievement to be proud of. However, there is still a shortage of organs for transplant. In 2011-12, sadly, 37 people in Wales died while waiting for an organ.

“I believe the time has come to introduce a change in the law, together with an extensive communication and education programme encouraging people to make a decision, and to ensure their families know their wishes.”

Griffiths said deemed consent will not apply to everyone – there will be safeguards for children, people who “lack capacity” and those who do not live permanently in Wales. The government will hold consultations about the proposals until September.

As well as expressing concern about the ethics of the change, the Church in Wales said it was worried that the scheme would be complicated. It said: “Organ donation is a way of expressing solidarity with our fellow human beings and sharing with them the gift of life, even after our own death. Signing up to the organ donor register is something that all Christians should be encouraged to do. But, like any other altruistic gift, organ and tissue donation should be freely given, not assumed.

“We are pleased that the Welsh government has taken note of the responses made to the first stage of the consultation process. There is now much more clarity about the system, especially about recognising the importance of the involvement of families at the time of donation.

“However, the system that will have to be introduced to ensure that potential donors fulfil all the necessary criteria (residence, age, mental capacity, evidence of wishes, etc) will be complicated. It would be better to invest resources in widereaching public awareness campaigns to encourage more people to become voluntary donors.

“Evidence that any system of ‘automatic’ donation increases the supply of organs – whether it’s called ‘presumed’ consent, ‘deemed’ consent or ‘opt out’ – is still disputable.”

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