Only irrational persons could imply that there was any interest on finding the McCann guilty.
For Portugal it would be more comfortable to consider as true the fantasy created by the McCann. A strange abductor that takes a little child away would, politically, be much easier to deal with than trying to find out the truth about a shameful crime committed inside our borders.
If it wasn't for a bunch of motivated policemen, the politicians would have traded the life of a child by the commodity of allowing it to go unquestioned, as was the wish of UK´s prime ministers (Blair, Gordon and now Cameron).
I think it is far more likely to have been the other way round. Given how much British holiday-makers contribute to the Portuguese economy, it would have been an unfortunate outcome to find that an abductor had taken a holiday-maker's child from her bed, particularly if it had turned out to be a Portuguese abductor. Much better to put the emphasis of the investigation on the parents of the child - to imply (as happened in fact) that these
British parents had done away with the
British child. Not Portugal's problem.
If political pressure was ever brought to bear, it is more likely to have come from Portugal than from Britain.