London on £25 a day

• £0.02 : earplugs
• £16: room in a flatshare with 3 others in far East London.
• £1.50 : power smoothie breakfast
• £3 : Tesco lunch
• £1.50 : Peter Special dinner
• £1 : Misc (toiletries, friends, whatevs)
• £0.40 : supplements (amortized)
• £0.40 : bike maintenance (2 x 6 miles per day commute is hard on it) (amortized)
• £0.30 : charity shop clothes (amortized)
• £0.20 : internet
• £0.00 : council tax (included in rent)
• £0.00 : library books
• £0.10 : electricity
• £0.00 : heating. it's London.

This isn't a minimal per diem - you could live in a car, or benefit from nepotism of some sort - but pretty optimal in 4D nutrition/comfort/employability/thrift space.