"We will look at is as a merger. Our mergers team will look at the market share and the impact on competition, and if it feels there are concerns we will launch a formal process," a spokesman said.
Sky's shock move last Friday has been met with uproar by NTL, which had been planning a £5bn bid to merge with ITV.
The cable firm, soon to rebrand as Virgin Media, claims the purchase is a blatant bid to block its move to create a strong opponent to the satellite giant in the marketplace.