Thanks to those of you who pointed out that the best way of getting over the heat is to ... wait for a day, and watch London go back to being rather cold and British. And also to those who noticed that 30 degrees hardly constitutes a proper heat wave - perhaps 40 would be more like it. Still, us British have got to dream at least that we live in the tropics every now and then.
But anyway - I'll certainly come away with one really good tip from Catherine - put your water bottle in the freezer an hour or two before setting off on your journey - and hey presto, an ice cold drink all the way home.
Happy cycling everyone.