People who abuse children and try to escape unpunished by staying silent or blaming someone else will face up to 10 years in prison from next week, Kenneth Clarke has said.
The loophole will be closed by extending the offence of causing or allowing the death of a child, which was used to prosecute Baby P's killers, to cover causing or allowing serious physical harm, such as brain damage or broken bones, the Justice Secretary said.
It follows a number of cases where prosecutions could not be brought because it was impossible to identify the individual responsible for the abuse.
This included the cases of a five-month-old baby who suffered a brain haemorrhage and fractured skull and a two-week-old with a broken collar bone, ribs and leg, the Ministry of Justice said.
No-one was charged in either case, but the injuries were not thought to be accidental.
"By making sure this Bill became law we have taken the opportunity to close a terrible loophole which has, until now, allowed people accused of seriously harming a child or vulnerable adult to escape unpunished," Mr Clarke said.
"We want to do everything possible to ensure that the most vulnerable members of our society are kept safe in their homes, and those that abuse their power do not evade justice."
The new offence, the Domestic Violence, Crime and Victims (Amendment) Act 2012, will also apply where the victim is a vulnerable adult.
Tory MP Sir Paul Beresford, who introduced the Private Member's Bill which was backed by the Government, said: "This new legislation will ensure that fewer cases of abuse slip through the net and is another safeguard to protect some of the most vulnerable members of our society."
Andrew Flanagan, chief executive of the NSPCC, added: "This change in the law is a real victory for children and has the potential to bring many more child abusers to justice.
"Adults can no longer inflict horrific injuries on children and get away with it by staying silent or blaming each other."
Baby P, now named as Peter Connelly, was 17 months old when he died in Tottenham, north London, on August 3 2007.
He had suffered more than 50 injuries despite being on the at-risk register and receiving 60 visits from social workers, police and health professionals over eight months.
Peter's mother Tracey Connelly, her boyfriend Steven Barker, and his brother Jason Owen were jailed in May 2009 for causing or allowing the baby's death.