To not to hide from each other their findings. It is not the football game or a competition whose dad is stronger..
IMO the announcement on the end 'the joint teams of UK and PT polices have discovered... xyz' would sound much better in the eyes of the world..
And also it would give a good message to the criminals!
Police teams competing who's gonna solve it faster or better is a great playground for criminals.. and in these cases only the criminals win.
Another thought, VIXTE (Probably not a new one)..
If, for the sake of argument, Scotland Yard do come up with a lot of new information and make a lot of progress, that is going to make the original investigation look inadequate. SY coming up with a breakthrough seven or eight years later, when the PJ could not solve the crime at the time, would be embarrassing.
There is an innate tension in this co-operation situation, however healthy it may be in parts.
Another reason no to use the press to interfere, Lyall -no?