Well, I've made an expensive start because I'm using up some of the food I already have. So the damage for today is:
Breakfast - Crusty Roll = 29p, Salami = 75p. Total = £1.14
Lunch - M&S Pizzetta = £1.99, Tomato and Onion Salad. Windfall apple. Total = £1.99
Dinner - Ribeye steak = £3.00, cucumber salad. Total = £3.00
Total for day = £6.13. Not a very good start.

Also to be included in the amount spent should be some other items which may or may not see me through the two weeks, and the cost of which will not be itemised daily.
Organic Tea Bags (80) £1.29 (from Aldi)
Original Hovis Wheatgerm Bread £.97 (from Sainsbury's)
Organic Cream £.79 (Sainsbury's)
Organic Skimmed Milk £.81 (Sainsbury's)
2 Organic Lemons £.50
Quarter packet Organic Butter £.23 (this is what I have left at present - I'll have to buy more later).
Total = £4.59

Items from my vegetable garden, which for the purposes of this exercise will be deemed to be free are: tomatoes, French beans, vegetable spaghetti, sorrell, apples, cucumber, onions, chives. I doubt they'll last out the two weeks, though.

Total Spend so far £10.72
Amount left to spend £24.28

Update:
Closer inspection of my expensive organic lettuce has revealed that it's gone all manky, so I've thrown it out, and now have a further £1.59 to spend.