A team of detectives are to fly to Libya as part of the investigation into the murder of Pc Yvonne Fletcher in London 20 years ago.
Yvonne Fletcher was killed and 10 others injured
Pc Fletcher is thought to have been shot by a gunman inside the Libyan embassy as she helped police a protest on 17 April 1984.
Metropolitan police officers hope to speak suspects in the case.
On Thursday, Prime Minister Tony Blair flew to Tripoli for talks with the Libyan leader Colonel Muammar Gaddafi.
Pc Fletcher's killer is thought to have been smuggled out of the country claiming diplomatic immunity.
Foreign Secretary Jack Straw told BBC Radio 4's Today programme on Thursday that Metropolitan Police officers will travel to Libya on 3 April.
The Libyan authorities had been "tardy", the foreign secretary said.
"It is terrible and it remains something that is a daily, hourly, nightmare for the parents concerned, to whom I have spoken," he added.
Libya's failure to co-operate with the investigation into Pc Fletcher's killing was among Conservative objections to Mr Blair's mission.
Wpc Fletcher's killer is thought to have been taken out of the country
But her mother Queenie Fletcher, 70, expressed
cautious optimism that the visit might bring about progress.
She said: "I really don't know exactly how I feel about it yet. Maybe if something good comes out of it, then it'll be worth it.
"If perhaps the police can go out there, then that would be good but they've been told in the past that they could go there only for them to come back and change their minds.
"But we'll just have to wait and see."
A Scotland Yard spokesman said he would not discuss how many officers were going to Libya, how long they were staying or reveal any details of their trip.
But Metropolitan Police Commissioner Sir John Stevens told BBC News: "We will be pursuing witnesses we have not seen before and doing anything we can to bring these people to justice in the courts of this country."
The Metropolitan Police Federation, which last month said relations with Libya should not resume if there is no justice for Pc Fletcher, welcomed the move.
Chairman Glen Smyth said it was inconceivable the Libyans did not know who was responsible for her death.
He told BBC News Online: "What we would like to see is that officers can have access to the suspect and, if it transpires they can get sufficient evidence, for the Libyans to co-operate with extradition."
Film director Michael Winner, chairman of the Police Memorial Trust, echoed Mr Smyth's sentiments.
He said: "One hopes that one of these visits will include the handing over of the murderer as a final gesture to close the chapter on what happened before."
The last time Metropolitan Police officers went to Libya was in the summer of 2002, also in connection with this case.