From what I understand, red lipstick comes in three forms- yellow reds (which are progressively making their way from red to orange), blue reds (which progressively make their way from red to purple) and "true" reds, which (I think) progressively make their way from red to brown.
According to marie claire's book "hair and makeup"-
Fair Skin- nude, rosy brown, beige pink, and sheer red lip colors
Medium-Toned skin- berry tinted gloss, plum, reddish brown, sheer chocolate, and deep red lip colors
Olive Skin- natural lip colors like rosy beige, deep red, sheer brown
Dark Skin- red, burgundy, blackberry, peach, purple, and caramel
Asian Skin- raisin, plum with brown undertones, red, and mauve
Kevin Aucoin doesn't say anything in the way of picking a good lip color, but I think that's because he likes to expierement so much.
The way I found a good red was to go to the MAC counter and get the fabulously gay makeup guy to help me pick one- tried on about seven different colors to find the one I wanted. OH, you're in London, honey get thyself to a Sephoria! I know they have at least 365 different colors of lipstick in their signature line alone- take a friend and make some time to try on a lot of the different reds. Don't just pick a red based on what you've been told, just look at the colors and pick the reds that appeal to you! Try and get a salesperson to help- but only if they're competent and act like they've got some training in making someone look good.
good luck!