The Home Office said most ninja swords had a blade of between 14 and 24 inches (36 and 61 centimetres), with one straight cutting edge and a tanto style -- or sharply-angled -- tip.

From August 1, anyone caught in possession of a ninja sword in private could face six months in prison. That is set to rise to two years under forthcoming legislation.

There is already a penalty of up to four years in prison for carrying any weapon in public.

The ninja sword ban is the final part of the so-called Ronan's law, a raft of anti-knife crime measures introduced in parliament last month as part of the government's crime and policing bill.

The measures include making retailers report bulk or suspicious sales to police and a rise in jail terms to two years for selling weapons to children.

The law is named after teenager Ronan Kanda, who was murdered with a ninja sword in 2022 by two other teenagers in a case of mistaken identity.

- 'Destroying young lives' -

"Knife crime is destroying young lives as too many teenagers are being drawn into violence and it is far too easy for them to get hold of dangerous weapons," Home Secretary Yvette Cooper said.

"Ronan Kanda was just 16 when he was ruthlessly killed by two boys only a year older than him.

"Today we are introducing the final part of Ronan's law in his memory -- banning the ninja swords that his killers should never have been able to use," she added.

The ninja sword move follows a ban on "zombie" type knives and machetes introduced in September 2024.

Under that measure, knives with a blade more than eight inches long and those with a serrated cutting edge, which are often used by gangs, were banned.

Prime Minister Keir Starmer has called knife crime a "national crisis".

Ahead of the ninja sword ban there will be a month-long surrender scheme in July, the Home Office said.

Knife crime in England and Wales has been steadily rising since 2011, according to official government data.

Excluding the northern city of Manchester, in the year ending June 2024, there were 50,973 offences involving a sharp instrument compared to 36,000 in the year ending March 2011 -- a 41-percent increase.

Figures for national deaths from stabbings are hard to find. But 10 teenagers died in stabbings in London last year and 18 in 2023, the Metropolitan Police told AFP.