Has Bad company managed to knock the mighty Halo 3 off the top spot ?

Well in a word - No.

1 Halo 3
2 Call of Duty 4
3 GTA IV
4 Gears of War
5 Guitar Hero III
6 Rock Band
7 Battlefield: Bad Company
8 Too Human Demo
9 Tom Clancy's Rainbow Six Vegas 2
10 NCAA Football 09

Halo 3 is still riding High at the top of the charts.

Source