Robert Downey Jr and Jude Law's blockbuster sequel held off competition from Alvin and the Chipmunks: Chip-Wrecked to emerge as the number one movie over the December 16-18 weekend.
Arthur Christmas slips down a place to number three, last week's chart-topper Puss in Boots is at four and romantic comedy New Year's Eve rounds out the top five.
Elsewhere, family movies Hugo and Happy Feet Two continue their stay in the top ten, landing at numbers six and seven respectively.
Twilight: Breaking Dawn - Part 1 charts at number eight, and has now grossed £29.5 million in the UK since its release on November 18.
The UK box office top ten in full:
1. (-) Sherlock Holmes: A Game of Shadows - £3,827,697
2. (-) Alvin and the Chipmunks: Chip-Wrecked - £2,361,867
3. (2) Arthur Christmas - £1,345,238
4. (1) Puss in Boots - £1,297,998
5. (3) New Year's Eve - £846,761
6. (4) Hugo - £387,208
7. (5) Happy Feet Two - £343,563
8. (6) The Twilight Saga: Breaking Dawn - Part 1 - £327,253
9. (8) A Very Harold & Kumar 3D Christmas - £109,063
10. (7) My Week with Marilyn - £89,207
Watch Digital Spy's interview with Sherlock Holmes: A Game of Shadows star Stephen Fry below: