The study was carried out to examine the impact of internet traffic on electricity consumption as demand on the National Grid increases. Evidence from nearly 400 devices shows a peak hour from 10pm.
The authors state: "To the extent that this traffic is associated with viewing films or programmes, it suggests that mobile devices are used to prolong hours of 'TV watching', perhaps after the main TV set has been turned off."
It supports a warning from Professor David Spiegelhalter, from the University of Cambridge, that couples are less interested in sex because they watch more TV in bed. In 2016, he blamed figures showing falling rates of sex on the "mass of connectivity" we have now "compared with just a few years ago when the TV used to close down at half past ten".
The Lancaster researchers, whose work is published in the journal Energy Research and Social Science, asked some participants to keep diaries, which showed the new peak internet hour was driven by TV watching.
The study warned that the huge growth in streaming may make it harder to meet Britain's future peak winter electricity demands.
They may be the "Tinder generation" but a relatively high proportion of millennials have never had sex, say researchers.
One in eight 26-year-olds are virgins, according to a study of 16,000 people born in 1989-90 – a significant rise from previous generations when one in 20 was the norm.