The parents of Madeleine McCann claimed they were treated badly by Portuguese police from the start of the investigation into her disappearance, according to a secret Home Office report.
They eventually fell out with UK authorities too and later did not share with police information gathered by their own private investigators.
The revelations are contained in a report ordered by the then Home Secretary Alan Johnson who wanted to know if it was worth getting Scotland Yard involved after Portuguese officers closed their first investigation.
The report said: "It is clear that from the beginning the McCanns felt there was a lack of clarity and communication on the part of the Portuguese police.
"Despite the involvement of British consular staff, they were, by their own accounts, left for long periods without any updates or communication with the investigators.
"They state they were taken to the police station on more than one occasion and then left for hours waiting to speak to someone who never materialised.
"They describe this situation as inhumane, with no real consideration for their emotional and physical wellbeing."
The report, written by the Child Exploitation and Online Protection Centre, also said too many UK law enforcement agencies had rushed to help and caused chaos, and that frequent criticism of the Portuguese investigation led to accusations the UK was acting like "a colonial power".
The report said: "Clearly, the McCanns have had a turbulent relationship with both Portuguese and UK law enforcement. They now openly acknowledge that there is a distinct lack of trust between all parties."
Even before the end of the first Portuguese investigation, Kate and Gerry McCann used money collected by their Madeleine Fund to hire private investigators. They continued to use them for the three years before Scotland Yard got involved.
The report said: "It is clear that the McCanns and the private investigators working on their behalf have gathered a large amount of information during the course of their enquiries. This information does not appear to have been shared fully with the Leicestershire constabulary or the Portuguese authorities.
"It is imperative that they are encouraged and persuaded to share this information."
The report led to Scotland Yard launching a review and later its own investigation in 2011.
It recommended the setting up of a UK national centre for missing children to better coordinate the response when British children go missing abroad. That has never happened.
Mr Johnson supported the report's recommendation, but was voted out of office in the 2010 General Election.
He said: "Nothing's happened in the ensuing 10 years that suggests that if it happened again it would be an any better, more coordinated response."
:: Watch the documentary Searching For Madeleine on Sky 1 on Tuesday, 2 May at 10pm, and on Sky News on Wednesday, 3 May at 8pm.