Figures released this week by Google show a better-than-expected first quarter profit of $1.31bn (£650m), up 30 percent from the same period a year ago.
In a first for Google, 51 percent of total sales were made abroad and, according to BBC technology expert Rory Cellan-Jones, Google UK was responsible for $803m (£407m) of this.
In his blog Cellan-Jones said: "Last year, ITV's net advertising revenue was £1.5bn. So, even if you just multiply Google's earnings by four and assume no further growth this year, Britain's biggest commercial television business - the original 'licence to print money' - is about to be overtaken by an American upstart which arrived in the UK only in 2001.
"You could not ask for a starker example of the threat to traditional media from the online world."
He added: "The latest figures I've seen put total UK online ad spending at around £2.8bn last year, of which Google had nearly half. That's a stunning share, and with the acquisition of DoubleClick now completed, Google looks set to be bigger in display too."
Analysts have predicted that Google's strong performance could strengthen Microsoft's resolve to buy Yahoo, even if it means raising its $44.6bn (£22.3bn) offer.