It is relatively easy to live on a budget starting from a position where you have all relatively new stuff, and where you have a full closet of relatively new clothes.
Also: €25 for eating out once or twice plus clothes?
Tech was relatively decent (used X300, used X41, a weird desktopy-mediacentery thing) when I moved in, I got a T410s after two years from the money I had saved when the battery in the X300 failed and sold the latter for 500€ (350 after replacement of said battery). Trips to my parents were usually paid directly by them, but they obviously weren’t strictly necessary either.
You can get a döner and a drink or two for ~8 € – surely not eating out, but not eating in either.
[0] I spent about 25 € there per week, which would give 120 €/month for strictly groceries and a further 30€ for extras (cheap pans, clothes, paper etc.).
I also didn’t mean to imply that I had found an optimal solution, but merely a solution satisfying the constraints.
So I lived off (700 - 310 - 100 - 50 = 240 €)/month, which I found to be no particular problem – ~150 €/month on food, toothbrushes etc. (general groceries), 30 €/month on telecommunications, 35 €/month on electricity which left me with 25 €/month for eating out once or twice plus clothes.
Hence, I’d say that 7 £/day is perfectly possible, provided that rent is covered by other means (as it is for German long-term unemployment benefits of ~350 €/month).