The founders of Skype on Friday accused Michael Volpi, partner at Index Ventures, of stealing trade secrets, in an escalation of a complex legal battle with the group of venture capital investors seeking to buy the internet telephony company from Ebay.

Joost and Joltid, two companies owned by Skype founders Niklas Zennstrom and Janus Friis, filed a suit in a Delaware court against Mr Volpi and Index Ventures. They accuse Mr Volpi of abusing his position as a former chairman and chief executive of Joost, to steal key technical information.