Although that rises to 71% of smartphone owners.
31% of UK mobile owners used apps in June 2010, according to data shown to ME by comScore, taken from its MobiLens survey.
That means that out of 48.5 million mobile users here, 33.5 million didn't engage with apps in any way during that month.
This is all mobile owners, though. What about the comparison between smartphone and feature phone owners?
comScore has a stat for that too: 71% of smartphone owners in the UK used apps in June, but they only make up 28% of the UK base.
Only 15.2% of non-smartphone owners are using apps. Meanwhile, 37% of all UK mobile owners used their browser in June.
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"The takeaways are that anyone wanting to take their service or brand to mobile consumers needs to think carefully about how they do it," says Jeremy Copp, comScore's VP of mobile for Europe.
"An app isn't the automatic answer. You might want to consider a site, or use SMS, or a combination of all three. An app isn't a silver bullet to get you to everyone."
Update: Copp says comScore's research shows that usage of apps and the mobile internet is growing in the UK, as smartphone penetration increases.
In June 2009, 21.5% of UK mobile owners were using apps, and 52.3% of UK smartphone owners were. So year-on-year, growth has actually been strong.
"It's an early stage, and we're seeing rising consumer awareness, but for brands it's about understanding the goals of their marketing," says Copp.
"If you want to reach 65% of 18-35 year-olds, you're not going to do it just by building an app."
comScore's research also shows that maps, social networking and weather continue to be the three most popular app categories across the US and Western Europe in terms of usage.
