No one provider dominated, with EE coming out best in England, Vodafone the overall winner in Northern Ireland and Three in Scotland and Wales.

The study, from mobile network performance firm RootMetrics, also suggests that England has the highest amount of 4G while Wales trails behind.

Operators will bid for fresh spectrum for faster services later this year.

"These latest results have really shaken things up and show the increasing competitiveness in the UK, particularly over the last six months," said Scott Stonham, general manager of Europe for RootMetrics.

"EE continues to lead the way, but Three and Vodafone are close behind. What is clear is that each operator showed strong performance in at least one particular country, while nobody was able to sweep the board at the four-nations level.

"UK consumers have strong mobile options depending on how and where they use their devices most," he added.

The report assessed availability of 4G services across the UK, examining six categories, including network reliability, network speed and data performance.

• England - EE (91%), Vodafone (83%), O2 (82%), Three (69%)
• Northern Ireland - EE (90%), O2 (83%), Vodafone (80%), Three (61%)
• Scotland - EE (83%), O2 (80%), Vodafone (76%), Three (59%)
• Wales - EE (79%), Vodafone (60%), O2 (60%), Three (54%)

In the UK's 16 largest cities, EE received the highest scores in all categories. It was also judged the UK's overall best-performing network, due to England's larger population.

Three won the award for reliability.

Ian Fogg, an analyst at research firm IHS Markit said: "To succeed, mobile operators must balance the amount of spectrum they own with how they manage their networks."

Merger distraction

O2, which did not win in any category may have been hampered by its planned merger with Three, which was blocked.

"It may have been a distraction which meant things like discussions around network planning were put off," he said.

"Added to that, O2's challenge is that it has less spectrum than some of its competitors but a large customer base."

In response the company said: "We spend over £2 million every day improving network service and expanding coverage", adding "different network surveys produce different results".

Although 5G is still some years away from commercial availability, Ofcom is due to auction 3.4GHz spectrum in October, which will be used for the next generation of mobile networks.

The regulator has capped the amount of spectrum each operator can bid for. EE is not allowed to bid in the 2.3GHz category, which will be auctioned at the same time and can be used to enhance 4G.

EE currently has around 45% of the UK's usable spectrum, following its acquisition by BT, which bid for spectrum in 2013 even though it did not have a mobile division at the time.

Further auctions of spectrum suitable for 5G are expected in 2019.

The timeframe for the auctions could be delayed because of legal challenges from Three.