Coffee in London

My (somewhat limited) experience of London coffee leads me to wonder if it is in fact possible to find a decent latte in its midst. I am determined to find one nonetheless, no matter how far and wide I may need to search. I commit to cataloguing my success - and failure - in these (electronic) pages.
Meanwhile, since I have three months to go I might as well spend some time deciding how I rate coffee, ie, on what specifics I determine a coffee drinkable or otherwise.
Froth, for example, should be characterised by its sweet flavour and thick texture. The coffee itself should be rich and creamy and never stale. It should not be bitter, the beans over-roasted, or the strength overpowering.
I probably sound like a sycophantic snob at this point, but I believe in setting a standard dammit! I have had perfect cups of coffee: A latte from Cibo is almost always completely delectable. Cibo has sadly not yet spread to London, but I am confident that coffee connossieurs are to be found the world over, and thus must good coffee also follow.