This is fascinating. Given various folks' suggestion that I ought to come up with a notional figure for rent and deduct it (Pete's being the most recent and most thorough) I had a go. It only serves to further illustrate the unreality of my situation, living rent-free in a house three bedrooms too big for me. Or, being kinder, working from home in a house with study room and two spare bedrooms. And as rent on such a property would be at least £450pcm in this area (probably more as most rented properties round here are student houses) that's at least half my income.
I wrote yesterday that I realised my present lifestyle is unsustainable on mimimum wage. These latest calculations underline this starkly. No way I can lose half my income and survive, the way I live.
Anyway, given this debate and in the spirit of wanting to have a reasonably realistic experience this Lent, I've decided to take a ball-park figure and drop my income to £50/week. That brings me into line with a few of last year's participants, haven't seen any diaries for this year yet.