Parents are to be banned from physically punishing children under legislation being introduced on Monday by the Welsh government.

Ministers in Cardiff are hoping Wales will become the first country in the UK to stop fathers, mothers and other adults acting in a parental capacity from smacking children to punish them.

The law would remove the defence of “reasonable punishment” that has been in force since Victorian times in England and Wales.

The Welsh government insisted mothers and fathers would still be able to parent effectively. It said the proposed law would not stop a parent from grabbing a child about to step out into a busy road, or brushing a youngster’s hair against his or her will.

But it argued that the time when it was acceptable to strike a child to punish misbehaviour had gone.

Julie Morgan, the deputy minister for health and social services, said: “We are sending a clear message that the physical punishment of children is not acceptable in Wales.

“What may have been deemed as appropriate in the past is no longer acceptable. Our children must feel safe and be treated with dignity. The legislation will be accompanied by an awareness-raising campaign and support for parents.”

Research published last year found one in 10 parents in Wales said they had recently smacked a child to manage their behaviour. In 2015 it was one in five. According to the study, 81% disagreed with the statement “It is sometimes necessary to smack a naughty child.”

The bill is also significant because if enacted it will be seen as the first major divergence between Welsh and English law since Wales was given more lawmaking powers two years ago.

A private member’s bill to ban the physical punishment of children has been introduced in Scotland and it is not clear whether it or Wales will be the first to bring in a ban.

About 50 countries have already brought in a ban and another 50 are considering doing so, but there are no plans in England for a such a law.

Morgan added: “I don’t see any signs of the UK government doing this.” She has campaigned against smacking for 20 years as an assembly member and before that as MP for Cardiff North. “I think that they [the UK government] felt nervous about it, they felt the time was not right; it feels in Wales the time is right. I’m sure England will follow.”

The Children Wales bill was being introduced on Monday and is expected to receive cross-party support.

If passed, adults acting in a parental capacity will not be able to use the common law defence of reasonable punishment if accused of assault or battery against a child. The Welsh government said it would be up to citizens to decide if they should report a parent they saw smacking a child and down to the police and Crown Prosecution Service to judge whether to prosecute. But it said the proposed law was all about changing attitudes.

Physical punishment is already against the law in schools and other education settings. Removing the defence is seen as the last step in making the physical punishment of children illegal in all settings.

Welcoming the announcement, Sally Holland, children’s commissioner for Wales, said: “There’s nothing reasonable about physically punishing a child. This bill sends a clear signal that Wales is a country which protects children; a country which will afford children equal protection from physical punishment as adults; a country which promotes children’s rights.”

Viv Laing, head of policy at NSPCC Cymru, said: “It’s wrong that children in Wales have less protection from assault and that a legal defence which does not exist when an adult is hit can be used to justify striking a child.”

The defence of reasonable punishment has been in place in England and Wales since the notorious trial of the teacher Thomas Hopley in 1860, who beat a pupil to death. He was convicted of manslaughter but the judge said “moderate” corporal punishment was allowed to correct “what is evil in the child”.