Last night's show, screened by ITV, had an average of 4.6 million tuning in to see acts such as One Direction and Arctic Monkeys winning awards.
The figures matched those for 2006 when the show suffered a ratings collapse, but that year was also a pre-recorded programme. It has been broadcast live since 2007 because it was thought the spontaneity of seeing things as they happen would boost audiences.
The total for last night's broadcast also includes viewers watching on ITV's +1 catch-up service which was not available eight years ago, with only 4.2 million actually watching live.
The Brits, staged at London's O2 Arena and hosted by James Corden, had an audience last night which was the lowest for at least 15 years.
The 2013 show had achieved a 10-year high with 6.5 million and a peak of 7.5 million, while this year's peak was way down, at only five million.
TV chiefs took some comfort from the number of people who sent messages about the show last night, hitting what is said to be a new record of 4.14 million messages posted on Twitter.
It was way up on the 1.4 million who tweeted about the show in 2013, but in an analysis posted online by Twitter bosses, they say that half those comments were actually people taking part in the "social vote", which was introduced this year allowing fans around the world to choose who took the best video prize.
The number who tweeted about the show itself last night rose by a third, although the figures released by Twitter were for users around the world rather than just the UK. In addition to being screened by ITV, it was streamed internationally on YouTube which would have driven up the global tweets.
Unsurprisingly One Direction won the video vote, as with 17.8 million followers they had almost three times the number of the four other shortlisted acts in their category combined.