In the shade of a stained tarpaulin stretched across a dusty courtyard in Chalco, a desperately poor neighbourhood on the outskirts of Mexico City, María Guadalupe Fierros is collecting the weekly contributions of a group of friends who have taken out loans to fund their small businesses.

Ticking off the names of her friends as they make repayments, she stuffs the notes and coins into her syndicate’s makeshift treasury for safekeeping: a scuffed cardboard box with the words “Price Shoes – making the most of your fashion” on the side. With a broken-down car on one side of the courtyard piled high with egg cartons and cardboard, a wall covered in coils of hosepipe, with rusty metal and plastic crates on the other, the local meeting place may not look like much. But this is the visible face of the most dynamic area of Mexico’s banking sector: microfinance.