Pope Francis has taken the world by storm since his election to the papacy in March last year, and his popularity is now spreading according to retailers.

Pope-themed onesies, underpants and cuff-links are just some of the items the pope's fans can purchase. (Read more: Pope Francisattacks 'tyranny' of unfettered capitalism)

Luca Zennaro | AFP/Getty Images

The so-called "Francis effect" has sparked a boom in the sale of such merchandise in Britain and America, according to a report by the Catholic Herald. Retailers reported a 20 percent increase in the sale of hooded tops and t-shirts supporting the papacy, since Francis' election as Pope Benedict's successor in March last year. (Read more: Pope finds a new enemy—capitalism) Garments emblazoned with quotes from Pope Francis are the best selling items, with the slogan "rebel against culture" shifting the most merchandise, according Catholics With Attitude, a catholic clothing provider with offices in London and Glasgow. The quote comes from an address on Copacabana Beach, Rio de Janeiro, during the 2013 World Youth Day in where he called on young people to reject hedonism in favor of marriage and family life.