UK always gets stuff a while after the rest of the world...
It's a good thing anyway.... after the "overwhelming demand" () of Hold It Against Me there forcing it to be released immediately. It probably would've achieved a better peak had it just waited for the video and closer to the album like 99% of the releases there.
To be honest I think the song will peak on its 3rd or 4th week .... this week will be moderate, and the song will be increasing or being steady as the video gets released in a few weeks.