Grand Theft Auto IV managed to sell 609,000 copies in the UK on day 1.
Rockstar managed to knock the #2 game off, which was Grand Theft Auto: San Andreas at 501,000 copies.
As for the split across the consoles, the Xbox 360 version edged ahead with 335,000 to the PS3's 274,000. This is interesting because all predictions were looking like the PS3 would outsell the 360 version in the UK.
The 360 version also beat out Halo 3 for the fastest selling game on Microsoft's console. Halo 3 managed to move 266,000.
Shacknews: GTA 4 Sets One-day Sales Record in UK