A new BBC survey of 3G coverage has found gaps across the UK, showing that participants only had a signal for 75 per cent of the time on average, while only getting a 2G signal the rest of the time, according to the results published Wednesday.

"The data shows that, overall, people are getting 3G about three-quarters of the time, but coverage is nothing like as uniform as the picture painted in the coverage map issued by the mobile operators," the BBC's Rory Cellan-Jones said.

The gaps, also called 'notspots', extend across the UK, affecting London as well as other key towns, and cities the BBC said.

BBC published an interactive map , where people can enter their postcode to check their coverage at street level.

44,600 participants, using more than 270 device models, in 42 million locations were used, and the volunteers were asked to download an Epitro app to their Android devices that tracked the 3G coverage they were getting, the BBC reported.

"The BBC has undertaken a crowd-sourcing survey that is well beyond any scale seen by the mobile industry in this country or any other," Gavin John, chief executive of Epitiro, told the BBC.

"Over 44,000 volunteers from the Shetland Islands to the Isles of Scilly participated with 42 million locations tested from every county in England, Scotland, Wales and Northern Ireland."

"For the first time consumers have the means to see 3G coverage precisely where they live, work and travel," Gaviro added.

According to the survey, some of the worst places for mobile coverage are the UK's road and rail networks.

"A whole stretch of the A3 has little or no coverage and there are substantial blackspots when people are travelling," Juniper Research's Windsor Holden told the BBC.

"Mobile's key advantage is that you should be able to use it anytime and anywhere and that is not the case at the moment. There is no reason why coverage could not be improved in these areas," he added.

The results of the BBC survey back an Ofcom research published in May, titled the Measuring Mobile Broadband in the UK (PDF) which found "the availability of 2G, 3G or HSPA networks, and the performance delivered, vary significantly even within small geographic areas."