The grandma of missing British toddler Madeline McCann has come out hitting against the girl's parents, asking them where they were and why she was left alone.

Madeline McCann is suspected of being abducted last year while holidaying with her family in the Portuguese resort town of Praia da Luz, with this month marking the one year anniversary of her disappearance.

A wide reaching media campaign across Europe has since ensued, with parents Kate and Gerry McCann appealing to the public for help in finding their daughter.

However Maddie's grandma has since appeared to criticize Kate and Gerry's decision to leave their daughter unattended inside their holiday apartment while dining about 50-metres away.

The couple have faced questioning over their motives for leaving their children behind in an unlocked holiday home.

Grandma Susan Healy says the first thing she asked was where they had been at the time of her disappearance.

"Why did they think it was okay to do this... where were you?" she said during an interview marking the first anniversary.

Mrs Healy said that she was dumbfounded over why the couple had left their children alone at the apartment.

"I can read articles that say Kate and Gerry should never have left their children and I can accept that," she said.

"You find yourself over and over again in your head thinking, 'Why did they think it would be all right? Why did they think, all of them, it was okay to do this?'".

The couple remain the subject of a police investigation, and could also be charged with neglect.