Are you serious? Welfare + healthcare + pensions = 7.6 * defence in 2012[1]. People say cut Trident, well Trident is a rounding error. You could pay for it out of the NHS IT budget alone!
http://www.usgovernmentspending.com/
http://www.ukpublicspending.co.uk
http://usgovernmentrevenue.com
http://www.usfederalbailout.com/program_details
Any politician truly interested in transparent government will pay this guy a salary (job description: "same thing you always did, but more"), and maybe even give him a few hacker underlings and a web designer. His sites are ugly but awesome.
From your description, it sounds as if motters' description of "one highly precarious situation to the next" was incorrect.
Also, some parts of the UK are significantly cheaper than others -- i'd argue that you might be successful keeping yourself stable in the north or middle of england, but you'd struggle in london or it's outer reaches.
One more thing- people don't 'opt' to be in this situation usually, so they are quite likely to enter into it with a reasonable chunk of unsecured loans and such that'll suck up the money.
So, sure. You can be a college grad who's not yet got anything but student loans, and happily enter in to benefits to support you whilst you build something interesting... But as soon as you need to go anywhere or spend any money to further your goals, you might find yourself pretty stuck.
Of course there are many areas of the UK which are not poor and have a very high standard of living by international standards, so it's certainly not true that everyone lives like this.
Ok, I think I understand what you mean by "precarious". It sounds as if the poor have a stable level of consumption (or at least a stable minimum level of consumption), but the specific manner in which that consumption is paid for can vary significantly - one week benefits, the next week employment. Also a high risk of crime, due to inadequate police protection. Is that a fair assessment of what you mean by "precarious"?
Now for some reason, the weekly variability of income and the risk of crime causes the poor to value an infinitesimal chance at large sums of money a more strongly than immediate and certain consumption. Assuming the poor are being rational here (rather than simply innumerate), this suggests that the poor assign a very low value to additional consumption, or perhaps a very high value to purely psychological benefits.
I have a suggestion for improving the lot of the poor in the UK: your government should sell more lottery tickets and use the profits to pay for additional policing. Perhaps you should also try to encourage microfinance - in the US, nonviolent microfinance outfits offering "payday loans" have pretty much pushed loansharks out of the market.
The government were given the chance to have the lottery run for free by a group headed by Richard Branson - they chose instead to maintain the current incumbent who take 5% of gross takings ... that could have paid off some tax bills ...
The main benefit you can receive indefinitely if you're poor is a housing allowance, which is equivalent to your full rent (if you have low enough income/assets), capped at the 30th-percentile rate for rents in your area, for an accomodation suitable for your family size. For a single person, that maxes out at $400-600/mo, depending on what part of the UK you live in.
For cash benefits, there is a jobseeker's allowance, which you can receive if you show you're actively seeking work, participate in some mandatory programs to do so, and have a mandatory progress meeting every two weeks (and meet some other miscellaneous requirements that keep getting added). That has a max of about $100/wk for a single person.