The Series 2 premiere “Merger” was watched by 4.93 million viewers. It aired on 30 September 2002 as the first episode of the second series of the original British The Office.
The episode introduces Neil Godwin and several employees from Wernham Hogg’s Swindon branch, who arrive at the Slough office after management changes. David Brent immediately feels threatened when the newcomers respond more positively to Neil’s leadership than to his own.
The figures in the question are easy to mix up because the same episode table lists every Series 2 broadcast in order. “Appraisals” drew 3.94 million viewers, “Charity” drew 4.29 million, and the first Christmas special later reached 7.17 million. Those numbers belong to different episodes, not “Merger.”
The British series ran for two six-episode series, followed by two Christmas specials. Unlike the American remake, the original programme was broadcast by the BBC and used the documentary-style setting of Wernham Hogg’s Slough branch.