Virgin Media says it recorded the "biggest download day on record" on the same day as the latest Call of Duty update.
The average user downloaded more than 20GB (gigabytes) on 25 February.
Call of Duty: Warzone is known in the industry for its huge download sizes, and the update in question clocked in at up to 26.5 GB for some users.
BT also said that day was immensely busy, but not quite a record on its network.
Unlike Virgin, BT's provided data about the network as a whole rather than the average used by individual customers. It said the surge it saw, driven by both the Call of Duty patch and the live streaming of four European football games, hit a peak network traffic of 20.86 Tbps (terabits per second). It had seen Christmas peaks of above 21 Tbps.
Virgin, however, said its traffic record reflected a constant increase since the first pandemic lockdown.
The first lockdown saw a sudden burst of activity on home broadband networks, prompting fears that the national network would be unable to cope - fears which proved to be unfounded, as systems stayed largely stable.
During January and February's cold snap, usage was up 7.4GB a day compared with the same months last year, pre-lockdown.
But Virgin says downloads are up in the current lockdown compared with the first in 2020, with the average user downloading an extra 3.1GB a day.
Habits have changed too, with weekday afternoons between 14:00 and 16:00 becoming the busiest period for "upstream traffic" - that is, sending data to the internet, whether through emails, uploads or video calls - for the first time
The information was based on an analysis of some five million broadband customers' accounts, the company said.
One caveat is that the amount of data being pushed through the nation's broadband networks is constantly growing as demand increases.
Mark Jackson, editor of industry site ISPreview, wrote that "demand for data is constantly rising and so new peaks of usage are being set all the time".
Usage typically went up by 30% or more each year, he added.
However, Covid-19 lockdowns have accelerated that trend as demand has shifted away from offices to home broadband users. Video calls, remote learning and other high-data usage have also risen.
Gaming also makes a big contribution, due to the fact that many gamers download all their titles rather than buying discs these days - and even those who do prefer physical copies need to download large updates on a constant basis.
In November, the launch of new Xbox consoles led to a previous record being set by several internet providers as gamers downloaded the required data for the shift to next-generation gaming.
Call of Duty: Warzone, the popular battle royale shooter, is a well-known contributor to such statistics. Its minimum requirements for PC gamers include having 175GB of free space - a huge chunk of most computers' storage space.
PlayStation 4 owners have even been advised that they may need to delete some of the game's own data packs in order to download new updates and have them fit on the console's 500GB hard drive.