A lone woman armed with a whistle and enormous courage has set herself the task of defending unsuspecting tourists from the pickpockets who plague Barcelona.

Eliana Guerrero became so incensed by the way groups of thieves were able to freely roam the city's underground network that she now patrols the metro on her own.

She gives loud blasts on her whistle whenever she sees the thieves, who operate mostly in a dozen city centre stations including the Sagrada Familia and Placa Catalunya, and hands out flyers warning about the criminals.