1. Grand Theft Auto V (361,312)
2. FIFA 19 (360,588)
3. Tom Clancy's The Division 2 (263,520)
4. Red Dead Redemption 2 (259,931)
5. Resident Evil 2 (239,495)
6. Days Gone (229,182)
7. Tom Clancy's Rainbow Six Siege (175,451)
8. Call of Duty: Black Ops 4 (172,065)
9. Anthem (165,746)
10. Forza Horizon 4 (144,790)

"ERA's sources for games data includes ISFE and B2Boost for physical, and IHS Markit estimates for digital."

Source:

https://www.gamesindustry.biz/articles/2019-08-08-uk-spent-1-6bn-on-video-games-in-the-first-half-of-2019

Interesting. Kind of funny that GTA5 outsold RDR2 (and everything else). GTA5 even outsold FIFA. The PS4 and XB1 really are just GTA machines, that happen to play other games as well.

Seriously, who doesn't have GTA V and wants to play it by this point?

Correction: GTA and Fifa machines

People who just had their nuts hang for the first time. 

There's not enough of them to account for all the sales, though it comes relatively close.

https://twistedvoxel.com/days-gone-second-best-selling-uk/

This article gives data of first 7 months.
That is , ending July 31st 2019
Surprisingly, Days gone is now at 2nd place
by 31st July.

GTA5 is a 6 year old game and it still outsold FIFA19.  I stand by my original statement.  The PS4 and XB1 really are just GTA machines that happen to play other games as well.

Not everyone buys a new Fifa every year. And those who do tend to do so very close to release.