The animated sequel opened to £853,226, making it the first movie to debut in the number one spot with less than £1 million since 2010's The Other Guys.
Ice Age 4 opened in Republic of Ireland, Northern Ireland and Scotland on Friday (June 29) to coincide with the school holiday. Its slim location count - just 134 - will be boosted when it is released in England and Wales on July 13.
Prometheus climbs up two places to occupy the number two spot, romantic comedy The Five-Year Engagement holds on to third place, Men in Black 3 is at four and Kristen Stewart's Snow White and the Huntsman is a non-mover at five.
Last week's chart-topper Abraham Lincoln: Vampire Hunter experiences a sharp 65% drop in ticket sales as it tumbles down to number six.
Elsewhere, the only other new release to make it into the top ten is William Friedkin's Killer Joe.
The UK box office top ten in full:
1. (-) Ice Age 4: Continental Drift - £853,226
2. (4) Prometheus - £750,652
3. (3) The Five-Year Engagement - £745,400
4. (2) Men in Black 3 - £727,787
5. (5) Snow White and the Huntsman - £606,624
6. (1) Abraham Lincoln: Vampire Hunter - £386,743
7. (-) Friends with Kids - £357,520
8. (7) Chernobyl Diaries - £284,530
9. (6) Rock of Ages - £240,445
10. (-) Killer Joe - £208,553
Watch the Ice Age 4: Continental Drift trailer below: