The UK policing agency that advised Portuguese detectives to consider the possibility of the McCanns' involvement in their daughter Madeleine's disappearance said yesterday this was common practice.
The comments came after it emerged in a Lisbon court on Wednesday that the National Policing Improvement Agency recommended police investigate Gerry and Kate McCann.
The revelation was made by lawyers for former Portuguese detective Goncalo Amaral, who is fighting to overturn a judge's ban on his book about the case.
An agency spokesman said: "In disappearance cases it is common for the NPIA to advise investigating officers to consider the possibility of the involvement of family and close friends. This is good practice for investigating such cases.
"The NPIA gave similar generic advice to the Portuguese police in the Madeleine McCann case."
Madeleine's parents will have to wait until next week to find out if Mr Amaral has succeeded in overturning the book ban after the court hearing ended without a decision on Wednesday.
The McCanns, from Rothley, Leicestershire, were in Lisbon to continue their battle to stop the former senior detective repeating claims that Madeleine is dead.
Mr Amaral was the first head of the police investigation into the girl's disappearance from Praia da Luz in Portugal in May 2007, shortly before her fourth birthday.
In July 2008 he published a book, Maddie: The Truth Of The Lie, which alleges that Madeleine died in her family's holiday flat and that her parents faked her abduction.
A judge granted the McCanns a temporary injunction in September last year halting further sale or publication of Mr Amaral's book and a TV documentary he made about the case.
The ex-policeman launched an appeal against the ban in a Lisbon court last month.