I really like the announcer voice that’s currently in place. It’s calm, lightly sarcastic and it has a nice accent going which really suits the setting. However, this guy reminded me of a milder version of Totalbiscuit (aka The Cynical Brit).
Currently Totalbiscuit is the biggest game reviewer around, bigger than Yahtzee I would even say and that makes him incredibly influential.
So with the game set in London and the Britishness of the game leaking from its pores I think it would be a great idea to hire Totalbiscuit and let hem do all the announcer voices.
Here’s his Youtube version http://www.youtube.com/user/totalhalibut
And with that idea planted, you can even expand on it further by hiring more popular youtube gamers and let them do character voices. This is absolutely blatant pandering to the pc gamer public but its an incredible way to build hype and I think it would generate more exposure than when that money would be spend on unknown voice actors.
Maybe let Yahtzee do one side and Totalbiscuit the other. Even more fun. I can already envision promo material of perhaps these two sworn (ingame) enemies as leaders of each team having a really brooding phone-call about the current state of London or something.