As the name suggests you are free to roam the streets of London without any missions to complete. The police and gangs will still chase you at times and try to arrest you, shoot you, ram you off the road etc. but not nearly as much as they would during the mission mode.
Unfortunately there are no inside areas like buildings or houses accessible to explore in free roam mode which is a bit dissapointing but most players like myself I think will still find plenty of things to do that make free roaming a rewarding and fun part of the game.
If you don't want to wait until you finish the game to get to cruise around the city with complete freedom there is a cheat that unlocks Free Roaming for you.
Unlock Free Roaming:
During the game intro press TRIANGLE, TRIANGLE, TRIANGLE, LEFT, SQUARE, TRIANGLE, TRIANGLE, TRIANGLE, LEFT, CIRCLE.
Below I have included some images further explaining how to do this and how to select free roam.
Enter the code during the intro.
If you entered the code correctly you should see a green hued screen for a few seconds and hear the sound of a woman groaning/screaming.
Select extra features from the main menu.
You can now use free roaming mode and view the credits if you wish.
You play Free Roaming as Mark Hammond and you start out straight away driving one of the "hidden" or "secret" cars in the game, the Lotus Super 7 MKII.
Mark Hammond in the Lotus Super 7 at the start location.
You start out facing east on Great Marlborough Street in Soho. You most likely start out here because Sony Computer Entertainment Europe's London Studio and Sony Music offices are located on the north side of this street.
Here you can see where you start in the Lotus Super 7.
Courthouse Kempinski Hotel
(19-21 Great Marlborough Street)
Next building to the right.
Next building to the right.
Possibly 13 Great Marlborough Street (see info below)
You can see the blue 'Sony Music' sign on the building.
Sony Music Entertainment
(10 Great Marlborough Street)
There are listings for SCEE at 10 Great Marlborough Street (same adress for Sony Music), so if they share the same building I wonder why they decided to only have "Sony Music" displayed on the building in the game?
There is also a listing for SCEE Technology Group at 13 Great Marlborough Street London, which would be one of the buildings above (somewhere between Sony Music and the Courthouse Kempinski Hotel).
Whatever the case it seems the starting point has been chosen due to the streets connection with Sony.
