Kate and Gerry McCann today criticised the "heartbreaking" failure by police to investigate new leads in their daughter Madeleine's disappearance as they called for a full case review.
The couple said they should not be forced to "beg" for co-operation between the British and Portuguese authorities.
Speaking the day after a court upheld a ban on a book in which a former detective claims Madeleine is dead, the McCanns appealed for fresh help from officials to find their daughter.
Mr McCann said: "You would hope that the parents of a missing child shouldn't have to be here begging for such assistance and that the authorities would actually do everything in their power in the first place."
The couple, both 41 and from Rothley, Leicestershire, have employed a series of private detectives to search for their daughter since she went missing from Praia da Luz in southern Portugal in May 2007.
They said there were cases where their investigators had passed leads on to the Portuguese authorities and Leicestershire Police, their local force, only for them to be ignored.
Mr McCann told a press conference in London: "There are certainly instances where information which we think is very credible and worthy of further investigation has not been actioned.
"We're gutted, it's absolutely shocking and difficult.
"We're trying our absolute best, Madeleine's still missing, and as we say the perpetrator's still there.
"We're not saying they are the leads that will result in finding her. But if you don't investigate information when it comes in, you will never solve it."
His wife added: "It's heartbreaking, to be honest."
Asked about how Leicestershire Police and other authorities responded to requests for a full independent review of the case, Mr McCann said the couple had encountered "reluctance".
He said: "It's a very serious case and there's lots of information that's being held currently by different law enforcement agencies.
"The information isn't even on a single database that people can search.
"We don't think there's been a systematic review of all the information and the leads, and that's something that would be automatically done in the United Kingdom.
"I think for a missing British citizen, that's what we're looking for.
"We want the authorities to work together. It is an international case, and always has been. We feel that it is fundamental to try to find Madeleine for a systematic review to take place."
He added: "I think people are reluctant to undertake a review because there's been difficult, sensitive issues.
"But Madeleine's rights should be put first. She's missing, she's innocent, and whoever's taken her is still out there, and that has to be of paramount importance."
Mr McCann said the authorities had done hardly anything to look for Madeleine since the Portuguese investigation was shelved in July 2008.
"If you look at since the file has been closed what's actually been done, and that's next to nothing - and that's for probably the highest-profile missing child case in Europe ever," he said.
Mr McCann revealed that the couple had contacted the Home Office to ask for help in improving working between British and Portuguese authorities.
He also suggested that any decision to carry out a review of the case would have to be taken at a very high level.
Mr McCann said it was beyond the scope of Detective Superintendent Stuart Prior, who led the British end of the Madeleine investigation for Leicestershire Police.
"I don't think Stuart has the power to make the decision. It has to come from higher up than that," he said.
"My feeling is they think it's quite difficult."
His wife added: "It is difficult but personally I don't think that's a reason not to do it."
The couple also welcomed yesterday's court ruling in Lisbon maintaining a ban on former Portuguese detective Goncalo Amaral's book, Maddie: The Truth Of The Lie.
The book alleges that the little girl died in her family's holiday flat and that her parents faked her abduction - something they strongly deny.
The McCanns said their main motive for challenging Mr Amaral was the fear that people would stop looking for Madeleine if they thought she was dead.
The couple are also seeking 1.2 million euros (£1.08 million) in compensation for defamation in separate civil proceedings against the former policeman in Portugal.Reuse content