The London Games are off to a smashing ratings start — on both sides of the Pond.

NBC’s primetime coverage of the Opening Ceremonies on Friday drew a whopping 40.7 million, according to Nielsen, making it the most-watched kickoff to the Summer Games on record. And auds continued to tune in at exceptionally high levels as action got under way Saturday night.

In Blighty, meanwhile, an average aud of 22.4 million watched the BBC’s live telecast — for a whopping 82.5% audience share — making the Olympics opener the most popular program on British television in 14 years. Viewing levels on BBC1 peaked at 9:50 p.m., when a massive 26.9 million viewers tuned in.

“BBC1 is all about bringing the nation together for its biggest moments, and I’m thrilled by the huge audiences who tuned in to watch this historic event,” said BBC1 controller Danny Cohen. “Danny Boyle’s opening ceremony was an absolute triumph.”

For the record books, this was the biggest aud on the pubcaster’s flagship web since a Christmas edition of sitcom “Only Fools and Horses” was watched by 24.4 million in 1996.

The average audience was also the highest for any British telecast since 23.8 million viewed the soccer game that saw England fall to Argentina in the 1998 World Cup on ITV.

In the States, Friday’s tune-in was nearly 6 million larger than for Beijing in 2008 and bested by nearly 1 million the previous high for a Summer Olympics kickoff, set by the Atlanta Games in 1996 (39.8 million).

In household rating/share, Friday’s opener averaged a big 21.0/37, the best for a non-U.S. Summer Olympics ever and the second best for a non-U.S. Games (summer or winter) in 36 years — since Innsbruck in February 1976 (23.2/37 on ABC).

While population gains account for some of the record-setting total-viewer count, the household rating for Friday night — with more than one-fifth of the nation’s TV homes watching — is particularly impressive considering how many more viewing options there are than in previous decades.

The 21.0 household rating is the highest for any network on a Friday night since the Opening Ceremony of the Salt Lake City Games in February 2002 (25.2).

The top local-market scores Friday night were a 27.8 household rating/49 share in San Diego and a 26.8/48 for both Washington, D.C. and West Palm Beach. Highest-rated among the top 10 markets was Boston (24.8/45), followed by two cities that have hosted the Summer Games over the last 30 years: Los Angeles (24.2/44) and Atlanta (24.1/39).

On Saturday, Nielsen estimates that NBC’s 8:30-11:30 p.m. portion of coverage averaged 28.7 million viewers — the largest crowd on record for any Summer Olympics. By comparison, the first Saturday from Beijing averaged 24.0 million in 2008, while Athens drew 19.8 million in 2004; the previous high had been set by the Atlanta Games in 1996 (26.3 million).

NBC drew more than four times the combined audience on the night for ABC, CBS and Fox (roughly 7 million).

The household score Saturday (15.8/29) is the best for the opening night of competition since the Montreal Games in 1976.

NBC’s two-day primetime average of 35.6 million viewers is the best start to any Summer Olympics, more than two million more than Atlanta (33.3 million), and more than 6 million more viewers than Beijing (29.5 million).

The U.S. captured five medals on Saturday, including a gold for Ryan Lochte in a 400-meter individual medley battle of titans against Michael Phelps.

NBC and its cable brethren are expected to air more than 5,000 hours of coverage before the London Games close Aug. 12.