The widow of Pc Andrew Harper is due to meet the Home Secretary next month in an effort to harness major political support for a new law meaning those who kill emergency workers are jailed for life.
Lissie Harper, 29, said she was contacted by the Home Office to arrange face-to-face talks with Priti Patel.
Mrs Harper said she was “delighted” that the Home Secretary had agreed to a meeting, and that her campaign is “vital and urgent”.
“We don’t just need warm words, we need action,” she said.
More than 500,000 people have now signed an online petition calling for Harper’s Law. The landmark was reached shortly before 6pm on Wednesday, a week after the petition was launched.
Mrs Harper and her 28-year-old husband had been married for just four weeks when he and a Thames Valley Police colleague responded to a late-night burglary in Sulhamstead, Berkshire, in August last year.
Two of Pc Harper’s killers – 18-year-olds Albert Bowers and Jessie Cole – last week lodged applications with the Court of Appeal seeking permission to challenge their convictions and their 13-year prison sentences.
They were jailed alongside Henry Long, 19, who was handed a 16-year sentence.
All three were acquitted of murder during a trial at the Old Bailey but were sentenced for the lesser charge of manslaughter after Pc Harper got caught in a crane strap attached to the back of a car driven by Long, and was dragged to his death along dark country lanes.
A judiciary spokesman confirmed on Wednesday that the Court of Appeal will hear applications by Attorney General Suella Braverman to refer the jail terms under the unduly lenient sentence scheme on October 28.
The hearing will be presided over by the Lord Chief Justice Lord Burnett, the most senior judge in England and Wales.
No decision has yet been made as to when the court will hear applications from Bowers and Cole to appeal against their convictions and their sentences.
Mrs Harper this week contacted unions for hundreds of thousands of emergency services workers in an attempt to secure their backing for Harper’s Law.
In a statement on Wednesday, Mrs Harper said: “Our justice system is broken, and we need Harper’s Law to help fix it.
“I have witnessed first-hand the lenient and insufficient way in which the justice system deals with criminals who take the lives of our emergency workers.
“We need Harper’s Law to give the ultimate protection to our emergency services workers. They run towards danger to protect the public from harm.
“They go out every day and risk their lives to protect us. They deserve the ultimate protection in return.”
She added: “I plan to use the grief I have to endure to fuel this campaign and to create a legacy for Andrew that, instead of being about the way in which his life was taken and the people who stole it from him, is to make his legacy about a positive change in our country for the people he was proud to serve alongside.”
Pc Harper’s Thames Valley Police Federation colleague, Sergeant Andy Fiddler, who has been supporting Mrs Harper, said: “Those in society who hurt those there to protect us should be dealt with with the full force of the law and judicial system.
“By creating a new Harper’s Law we hope those loved ones of all emergency services workers who sadly have to go through what Lissie has been through in the future will soon get the justice that they rightly deserve.
“The law must be changed. We want to work with the Government, politicians of all parties and the fantastic British public on this.”
A Government spokesman said: “We are in touch with representatives for Lissie Harper and the Home Secretary and Justice Secretary hope to meet with her at the earliest opportunity.”