It may be harder to maintain but real grass will always win for me!

There is absolutely no argument here... real grass all the way.

For a London garden, probably artificial grass because you don't have to maintain it. looks great all seasons for people who just don't have the time!

it depends a lot on the light levels as well, a shady darkish site would better suit artificial grass but if there is enough light for real grass then it would be real grass for me. this is not only because it looks much nicer, feels nicer but also because it helps to support the local wildlife ie attracting birds into the garden and insects and is also better for the environment. it is also untrue that artificial grass requires no maintenance, ideally it should be lightly brushed/blown once per month ( more in the autumn and spring months if surrounded by trees and also needs spraying with herbicide ever few months to keep the weeds from taking hold

if maintenance is an issue for real grass, have a think about adding some wildflower turf to the area, looks stunning for the summer and needs cutting just once per year