Taliban fighters targeting British troops in Afghanistan are using the latest ‘internet phones’ to evade detection by MI6, security sources said last night.

Skype, a popular piece of consumer software that allows free calls to be made over the web, has been adopted by insurgents to communicate with cells strung out across the country.

Unlike traditional mobile calls, which can be monitored by RAF Nimrod spy planes, Skype calls – the commercial application of a technology called Voice Over Internet Protocol (VOIP) – are heavily encrypted.

Web of deceit: Taliban internet calls are hard to monitor

Voice calls are broken into millions of pieces of data before being sent down the line and reassembled by the other caller’s computer.

The British and American governments  are investing considerable resources to crack the codes, and in the UK the Government is introducing legislation to force internet service providers to log all web activity by subscribers, which could then be turned over to the security services on demand.

The disclosure comes as the 8,000 British troops in Afghanistan are facing attacks almost daily from an increasingly well co-ordinated Taliban.

‘The trouble with this technology is that it is easily available but devilishly hard to crack,’ the source said. ‘The technology can now be accessed on mobile internet devices and the country’s mobile phone network is expanding rapidly.’

Skype was created in 2003 and three years ago was bought by eBay for £1.4billion. It has 300million accounts and at any one time, more than 12million people are using the service.

Sir David Pepper, the head of GCHQ, the British Government’s top-secret listening post, has told MPs that internet calls are ‘seriously undermining’ his organisation’s ability to intercept communications.

Skype said last night it did not want to comment.