The unnamed mum reported it to Portuguese police at the time, but it is claimed they failed to search the area or take fingerprints.
Detectives investigating three-year-old Maddy’s disappearance have now interviewed the mum.
A source said: “British detectives are keen to establish whether Portuguese officers missed a crucial line of inquiry here.
“There is some confusion over why this was not taken more seriously.”
It was reported that the mum said she heard a noise late one night and caught the intruder heading for the cot.
The would-be-kidnapper fled the apartment, thought to be in an apartment in an Algarve resort north of Praia da Luz, where Maddy was taken.
The alleged incident happened in 2010 - three years after Maddy vanished from her bed while on holiday with her parents Kateand Gerry and twin brother and sister.
Scotland Yard detectives are still waiting for permission to quiz three ex-staff members at the complex where the McCanns of Rothley, Leics, stayed.
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