Thanks for the replies. I did a little reading in the mean time and you are all correct, haden, nt and cappacino.
There was one man who was an ex-MI5 agent, but was part of a private company formed after his service.
From this article in July of 2012, it appears that the
McCann's did not suppress the file, it was the British government:
"Madeleine McCann file kept secret ~ The Home Office is refusing to release secret files on the Madeleine McCann case to avoid diplomatic ructions with Portugal.
"The documents are believed to record discussions with the Metropolitan Police about sensitive details of the baffling case.
"Rejecting attempts by a newspaper to see the files, the Home Office said there would be 'specific detriment to the UKs relationship with Portugal' if they were released.
"It also claimed disclosure of three of the documents would 'stifle discussion' between officials.
"A Met review of the case was ordered last year after pressure from the Home Office and David Cameron.
"Sources said there were 'serious concerns' within the Met that they were investigating a 'foreign' case over which they had no jurisdiction.
"Madeleines parents Kate and Gerry McCann, of Rothley, Leicestershire, are convinced she is still alive. She was taken in May 2007 from a holiday apartment on the Algarve."
http://www.express.co.uk/news/uk/329977/Madeleine-McCann-file-kept-secret
It seems there is always more to the story than scent.