TRhey did not teach you this in school?
Anyway
1a/ make nice medium-big prints of a wide range of your best photographs.
1b/ make business cards with, at a minimum, a mobile phone number where people can get in touch with you, plus the web address of your site
2/ put the pictures in a nice portfolio case, and if you can't find or afford a nice portfolio case, use your imagination (You've got lots, I know) to find some other way of carrying these pictures with style and panache.
3/ get some directories for London. Commercial and advertising photographers, design studios, daily newspapers, and, based on the pictures I looked at, style-related magazines. Look up their web sites, and make notes.
4/ get a London map, and mark the locations of all these places.
5/ get comfortable shoes (but stylish)
6/ Go, in person, with no appointment-making telephone call before hand, to the photographers on your list, and ask for permission to show them your shots, and if they won't look right then, ask for an appointment.
RELATED... you might also offer your services as a location scout and photo shoot organizer back in your home area. For this, shoot a variety of photos of places near home that would appeal to a fahshon photographer and a commercial photographer; use Photoshop of similar to fit six-eight shots on a sheet of 8x10 paper, along with your contact info.
If you can be helpful to a London photographer when you are home, perhaps it will inspire that photogapher to ask you to be helpful in London, too.
BAK