The number of carrier bags handed out to supermarket shoppers in the UK rose last year, for the second year in succession.

Supermarket shoppers used almost eight billion carrier bags in 2011, a increase of 5.4% on 2010’s 7.6 billion, according to the recycling group Wrap.

A major reason for this uplift is changing grocery shopping habits, with financial constraints upon households meaning families are doing several small shops a week, instead of one big trip. This, coupled with more people switching from using the car to public transport, means people are less likely to have reusable bags with them.

People doing several shops a week instead of one large shop has another implication for supermarkets. Loyalty. Doing a few smaller shops means people are likely to be shopping as they go about their everyday routines, and so also likely to shop at a few different supermarkets. Our research around loyalty (highlights can be found here) shows that Tesco and Waitrose are at most risk from shoppers switching. People shifting to more shops per week means smaller, in-town supermarkets are likely to benefit, as is the Co-Operative whose branches tend to be located close to where people live.