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It is the digital equivalent of a power blackout and the prospect is already worrying ministers and government planners - at some point in the next decade, the copper telephone network will run out of capacity.

Confronting the problem is expected to lie at the heart of Lord Carter of Barnes's Digital Britain review of communications policy, due early next year, with efforts to solve it focused on an unlikely source: mobile phones.

The Communications Minister is yet to reveal his plans, but he has been dropping heavy hints, writing in The Times this month that he wants to help to develop “mobile and wireless services that can do for broadband and video what they have done for the spoken word”.

His goal is to kick-start an auction of “fourth-generation” mobile technology, using a block of spectrum previously set aside for digital television. The 4G technology, known in the industry as LTE, or Long-Term Evolution, can deliver download speeds of ten megabits or more - five times quicker than a standard fixed broadband connection.

Joachim Horn, chief technology officer of T-Mobile International, believes that there is a need for fourth-generation technology because the mobile internet has been disappointing. “We are not able to deliver the speed and consumer experience for the applications coming out,” he said. “We need to accommodate higher use at a lower price.”

However, while the public sees fixed and mobile phone connections as quite separate, in Lord Carter's mind the two are linked. The governmental worry is that BT and other internet providers are not afraid enough - or in official speak “sufficiently incentivised” - to invest in upgrading fixed-line connections.

The risk is that, by the middle of the decade, internet capacity will stop increasing for many homes, just at the point where television and film are flying around the network. In October, 30.6million BBC programmes were streamed over the internet, which sounds impressive but is still a fraction of the total number of programme viewings for a typical night's television.

The threat of new, easy-to-deploy high-speed mobile technology will help. BT has promised to upgrade up to 40per cent of homes to fibre optic technology - where data is transmitted down filaments of glass at the speed of light - but the rest of the UK will be stuck on copper.

BT will use a new standard, ADSL2+, which promises speeds of “up to 24 megabits” - in theory ten times faster than the two-megabit standard of today. However, theory does not always match up to practice and other internet providers that use BT's network may not want to join it in investing to match its speed.

There are also similar worries about the behaviour of the existing mobile operators. Although three - Vodafone, T-Mobile and 3 - have upgraded their networks to one-megabit speeds, all operators are reluctant to invest heavily after the third-generation debacle, when the £22.5billion spent on licences never delivered.

Mike Short, president of the Mobile Data Association, said that operators would weigh up whether they bought spectrum or invested in new technologies, particularly in an economic downturn. “We're cautious about investing in spectrum unless there is proven demand,” he said.

As if to demonstrate the point, T-Mobile and O2 have taken Ofcom to court to prevent the regulator auctioning five parcels of spectrum at 2.6 gigahertz until it becomes clear what will happen to their existing mobile spectrum.

This 2.6 GHz spectrum can also be used for fourth-generation LTE services, but the relatively high frequency means that it requires more base stations, raising the cost of deploying a national network to £2billion, and coverage indoors is poor.

This weakness makes the separate television spectrum much more interesting. A chunk between 790 and 862 megahertz - “the sweetspot in the sweetspot” - has been identified by Ofcom. It would cost far less to deploy, provide better coverage indoors and, it is believed, give fourth-generation phones ten megabit-plus speeds.

Used at present for analogue broadcasting, the spectrum becomes available from 2012, although, in what appears to have been an error, some of it was assigned for use in free digital television.

Lord Carter's Digital Britain team is working on a way of moving the broadcasters elsewhere to free up the whole stretch between 790 and 862 MHz, with a view to auctioning it off in 2010 or 2011.

If the mobile broadband plan works, rapid internet development will continue into the next decade, fuelled by competing technologies. And, at last, it may be possible to watch Mamma Mia! on your mobile while sitting in a café.

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Making waves

Spectrum

Radio spectrum has a variety of uses depending on frequency. The lower the frequency, the greater distance a signal can spread, ideal for uses such as AM radio. Higher frequencies can handle more information but the range drops, ideal for Wi.Fi. In the middle lies the “sweetspot”, the UHF block, used for television broadcasts and mobile telephones.

The sweetspot in the sweetspot

Radio spectrum at frequencies between 790 and 862 megahertz, which combines both good bandwidth and medium range. Deemed ideal for high-speed mobile broadband.

LTE

Commonly known as fourth- generation mobile technology.

LTE, or long-term evolution, is seen as the most likely successor technology to third generation. Expected to deliver services at or slightly ahead of 10 megabits a second but is aiming for speeds ten times greater than that. Mobile phone operators are still testing

LTE and few have confirmed that they will use it for definite, with some interested in rival fast internet standard, WiMax.

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