Eleven medals were taken from the Grenadier Guardsman's home in Whetstone, north London, when he was in the property.
It came as world leaders gathered in Normandy on Friday's anniversary to pay tribute to those who fought and died in the Normandy landings.
A man with an Irish accent purportedly from a water company knocked on the pensioner's door and said he needed to check the water pressure, a Scotland Yard spokesperson said.
He was allowed in and appeared to look at the taps before leaving.
That evening the victim noticed items in his bedroom had been disturbed and 11 war and service medals had been stolen.
Nothing else is believed to have been taken and no arrests have been made, police said.
The man who entered the house is described as white, about 5ft 10in and of stocky build.
He spoke with an Irish accent and wore grey clothing that was similar to an engineer's outfit.
The veteran served mainly in Italy and North Africa.