I don't know how SY could have checked this out without going through the ILOR route, unless the PJ also wanted to check it out.
The tabloids seem to have been mainly interested in who was going to be named as arguidos, quite possibly as the term has sensationalistic connotations.
If the objective is to find out what happened to Madeleine and apprehend those responsible it is a shame that more effort hasn't been made to cut through the attendant red tape which surrounds international working.
IMO it is a waste of time and resources to have inquiries running in parallel even if relations between the two forces are excellent. The obvious thing to do is to set up a Joint Investigation Team (JIT) which would be a more efficient use of time by cutting the necessity of sending of letters for everything.
One can imagine it sometimes cuts the flow of an investigation as for example when the Met had to wait to see if their request to search the homes of suspects and have DNA samples taken was allowed.