I don't know offhand what proportion of the population have - and I agree that people shouldn't be excluded - but it is pretty common.

To expand the notion of benefits slightly, I got free school meals as a child; I got a full government grant to go to university; I've been on jobseekers' allowance (or whatever they were calling it that year) twice, and on income support for quite a long period.

If I could find a better metric for "not being permanently financially secure" I would.