My tyre's flat

... had to lock the bike up in front of Waterloo station and bus it back home. Will bus back there in the morning to get Evans to fix it... hope it's there :/

It may seem an odd question to you, but why don't you carry the minimum needed to repair a puncture?

Mini-pump
Spare tube
2 tyre levers
15mm spanner, or Multi-tool

Does that really take up too much space / weigh too much / stop you from looking cool?

EDIT: Some pertinient threads
Puncture Repairs
Carrying puncture repair stuff
If you can't change a puncture, don't fecking ride a bike