I get that question a lot, but it's possible so long as you're not spending on... well, anything. I've spent a lot of the last 2 years adjusting to not needing to buy things and disposing of luxuries (I wouldn't have called them luxuries at the time, but it's surprising how much isn't needed). What I do buy I find ways to acquire things very cheaply.

There are food blogs like this: http://www.theskintfoodie.com/ (Tip: Waste nothing, buy precisely what you need and plan how to use every bit)

You can get clothing from places like this: http://www.barone.co.uk/ (Tip: There's a huge supply chain from which you can purchase long before things hit shops)

I've turned off broadcast TV, cancelled the TV licence, and just watch on catch-up via iPlayer, etc.

Cycling cuts travel costs, though I keep a PAYG Oyster for when I'm with others and will make a journey with them.

And so on.