The track, which has spent a total of 12 weeks on the tally, clocks up a fifth non-consecutive week at the top after being knocked off a fortnight ago by Rihanna's 'S&M' remix.
Behind Perry, Adele remains at number two for a second week with 'Rolling In The Deep', while Britney Spears's 'Till The World Ends' remix, which features Nicki Minaj and Ke$ha, completes the top three.
Elsewhere in the top ten, Bruno Mars climbs from six to five with 'The Lazy Song', and Ke$ha shifts from nine to eight with 'Blow'.
Outside the top ten, Tinie Tempah's 'Written In The Stars' reaches a new peak at number 12, while Glee's 'I Feel Pretty/Unpretty' mash-up lands at number 22.
Martin Solveig and Dragonette's 'Hello' advances from 86 to 76, and Duck Sauce's 'Barbra Streisand' debuts at 89.
The top ten singles in full (click where possible for our reviews):
1. (1) Katy Perry ft. Kanye West: 'E.T.'
2. (2) Adele: 'Rolling In The Deep'
3. (11) Britney Spears ft. Nicki Minaj and Ke$ha: 'Till The World Ends' (Remix)
4. (3) Black Eyed Peas: 'Just Can't Get Enough'
5. (6) Bruno Mars: 'The Lazy Song'
6. (4) Rihanna ft. Britney Spears: 'S&M'
7. (7) Jennifer Lopez ft. Pitbull: 'On The Floor'
8. (9) Ke$ha: 'Blow'
9. (5) Jeremih ft. 50 Cent: 'Down On Me'
10. (8) Chris Brown ft. Lil Wayne and Busta Rhymes: 'Look At Me Now'