The UK's 4G networks are "poor" and lag behind the US, Europe and East Asia, according to new research.
While EE offers the best 4G network in the UK, with 61 per cent coverage, other countries are already achieving coverage of 70 per cent and higher, wireless mapping firm OpenSignal warned.
Its State of Mobile Networks: UK report, created with help from consumer comparison site Which?, rated the four nationwide UK mobile operators on their 4G performance and coverage.
Network upgrades made by Three saw its LTE performance tie with EE's, with both operators drawing for 4G download speeds and lowest 4G latency.
But Three's 4G coverage spanned just 40 per cent of the UK, leaving customers languishing on 3G networks much of the time.
O2 recorded a 56 per cent coverage for 4G, pipped by Vodafone, whose coverage reached 57 per cent.
O2 also scored poorly for 4G latency at 79 milliseconds, compared to EE and Three's 53 milliseconds and Vodafone's 64 milliseconds.
The report read: "While some countries are struggling to catch up with the rest of the world in 4G speed, the U.K. has an entirely different problem. UK LTE networks keep getting faster, but LTE coverage just isn't advancing at the same pace.
"While regulators and operators are already looking ahead to the 5G data networks of the future, mobile consumers today are still spending nearly half their time connected to 3G networks."
The report is based on research conducted via OpenSignal's app downloaded onto 31,525 people's mobile phones, which took place between November 2015 and January 2016.
It comes after Ofcom's own research identified EE as the UK's most reliable mobile network in December last year.
OpenSignal and Which?'s report also follows the Competition and Markets Authority (CMA)'s objections to Three's proposed 10.25 billion takeover of O2.
The EU's antitrust chief, Margarethe Vestager, is expected to block the current planned takeover after listening to the CMA, which claimed a merger would harm competition in the UK by reducing the number of operators from four to three.
Kester Mann, principal analyst at CCS Insight, covering operators, told IT Pro: "Hutchison is seeking to throw the kitchen sink to gain approval but it might have to do more as possibly facilitating a fourth operator, but that would certainly be its least desired outcome.
"It all comes down to how far it wants to go. If it really wants to do the deal, then it should be able to satisfy the Commission's concerns, but that may also erase many of the benefits of the deal. That's why it's really on a knife-edge."
