Originally Posted by
ClubClassCowboy
http://www.markuscoffee.com/
This is my favourite place to buy coffee in London. The owner has been there since 1957 and the roasting and packing machines are in the shop, so sometimes you can watch the whole process.
I recommend a 50/50 mix of Regent and Negresco for everyday filter coffee.
Be careful Tony Blair's armed police protection squad don't shoot you on the way out

Similar to Markus and quite near, Higgins in Duke Street (just South of Selfridges). Not sure where I heard it, but I heard they supply a number of embassies including the Italian one.