More websites are now loaded on smartphones and tablets than on desktop computers, a milestone that underlines how computing is rapidly shifting to mobile devices and which threatens companies reliant on traditional PCs.

Statcounter, a research company that tracks internet use across 2.5m websites, said 51.3pc of pages were loaded on mobile devices in October, the first time they have surpassed desktop and laptop computers.

This is up from less than 5pc in 2010 and less than 25pc three years ago. Smartphones accounted for 46.5pc of traffic, against 4.7pc for tablets.

The growth of high-speed mobile networks, more powerful smartphones and first-time sales in emerging markets have seen smartphones become many people’s most important, or only, computer.

Many industries that rely on the web have been challenged by the rise of mobile devices, which feature smaller screens and no keyboards.

Google, which has seen the value of advertising clicks decline because of smartphones, said last year that searches on mobile had overtaken those on the desktop.  Total spending on mobile advertising in Britain surpassed the PC in the first half of this year. PC sales have now fallen for eight consecutive quarters, the longest decline in the history of the industry.

Statcounter said that in mature markets such as the US and the UK, the desktop still accounts for the majority of web pages, but the gap is shrinking dramatically, while the mobile web has long been more popular in countries such as India, where it now accounts for 75pc of pages.

The data excludes the use of apps such as Facebook and WhatsApp, which account for a significant proportion of mobile internet usage.

Aodhan Cullen, Statcounter’s chief executive, warned that many small businesses and retailers have websites not designed for phones and tablets. “This should be a wake up call especially for small businesses, sole traders and professionals to make sure that their websites are mobile friendly. Many older websites are not,” he said.