Iglesias's 'I Like It' zooms from five to two this week, but is unable to dethrone Perry's 'California Gurls' - also number one in the US and Ireland at present - from the summit.
Meanwhile, rapper B.o.B. slips to three with 'Airplanes', his collaboration with Paramore singer Hayley Williams.
Eminem posts two singles in the top ten this week, climbing from eight to five with 'Love The Way You Lie', a duet with Rihanna, but slipping from seven to ten with 'Not Afraid'.
Notable gains outside the top ten come from Adam Lambert, who jumps from 18 to 12 with 'If I Had You', and Kylie Minogue, who rebounds from 30 to 18 with 'All The Lovers'.
The top ten singles in full (click where possible for our reviews):
1. (1) Katy Perry ft. Snoop Dogg: 'California Gurls'
2. (5) Enrique Iglesias ft. Pitbull: 'I Like It'
3. (2) B.o.B. ft. Hayley Williams: 'Airplanes'
4. (3) Uncle Kracker: 'Smile'
5. (8) Eminem ft. Rihanna: 'Love The Way You Lie'
6. (6) Travie McCoy ft. Bruno Mars: 'Billionaire'
7. (4) Usher ft. will.i.am: 'OMG'
8. (10) David Guetta & Chris Willis ft. Fergie & LMFAO: 'Gettin' Over You'
9. (9) Yolanda Be Cool & DCup: 'We Speak No Americano'
10. (7) Eminem: 'Not Afraid'