Lots of those needing to use the food banks are immigrants who are not entitled to any benefits. Some of these people resort to going through bins and eating other peoples waste. Others will be those who have lost their jobs or or otherwise experienced a major reduction in their wages and are using whatever income they may have remaining just barely keeping the payments on their mortgage up (even if claiming job seekers allowance, benefits will only pay for rent) so they don't lose their homes. Also, as one of those cases above illustrates, there can be long hold-ups for some benefit claimants, sometimes several months due to processing errors and sometimes needed paperwork has to go through lengthy appeals and so-on, during such periods there can be no income whatsoever.

Having said that I know numerous people on benefits, not one of them to my knowledge has ever felt the need to avail themselves of a food bank. I think such services are generally required by people who somehow slip through the net, such as above.