Virgin Media is celebrating the success of its trial 1.5Gbps broadband service, which it claims is the fastest cable connection in the world, 240 times higher than the national average for broadband in the United Kingdom. Virgin Media is keen to talk up the capabilities of its hybrid fibre-coaxial cable network. Although it reaches half the homes in the country, adoption of packages of 50Mbps or higher remains surprisingly low.

The trial service is being delivered to an area around Old Street in London, an area dubbed “Silicon Roundabout,” including the TechHub workspace for technology entrepreneurs.

Visiting TechHub, the communications minister Ed Vaizey, said: “It is fantastic to see the fastest internet speeds in the world over cable being trialled here in the UK.”

Using the same hybrid fibre-coaxial cable infrastructure as residential services, the technology trial offers 1.5Gbps downstream and 150Mbps upstream.

Multiple radiofrequency channels are bonded to deliver additional bandwidth for internet services. With characteristic hyperbole, Virgin Media says this provides “theoretically near infinite capacity,” a ridiculous claim carelessly repeated and reported by many who should know better. Similarly, people tend to talk about “fast” and “speed” when referring to transfer rates, or use Mb when they mean Mbps, or megabits per second, which in turn consumers often confuse with megabytes in file size.

The EuroDOCSIS 3.0 standard allows multiple 8MHz channels to be bonded, each capable of carrying over 50Mbps downstream. Although there is no stated limit to the number of channels that can be bundled, this is practically limited by the capability of modem hardware and the capacity of the cable, which typically carries signals in the 5MHz to 1000MHz frequency range. This bandwidth is also shared with other users in the neighbourhood. So like most communications networks, the capacity may be contended.

That said, research shows that on average Virgin Media customers can achieve close to the published rates in speed tests. For most users, performance is more likely to be limited by congestion elsewhere on the internet.

For residential customers, Virgin Media is currently able to deliver its 100Mbps service to over a quarter of homes in the United Kingdom. Its top tier package offers 100Mbps downstream and 10Mbps upstream and costs £45 a month as a standalone service. For the rest of its cable network, Virgin Media currently offers packages up to 50Mbps but is on track to upgrade this to 100Mbps by mid-2012, when it will be available to almost 13 million homes, nearly half the households in the country.

Virgin Media currently has just over 4 million cable broadband customers, but only a fifth of them subscribe to tiers of 20Mbps or above and only 150,000 of them were taking the 50Mbps package at the end of March 2011. Virgin Media signed up around 150,000 new broadband subscribers in the previous year. Nearly two-fifths of them took a 20Mbps or above tier, suggesting that higher capacity connections are a concern for some, but not everyone.

The national average broadband speed in the United Kingdom as reported by the communications regulator Ofcom at the end of 2010 was 6.2Mbps.