The European parliament has voted to formally invite Edward Snowden to give testimony on NSA spying, despite opposition from conservative MEPs. If the US whistleblower provides answers to the questions compiled by parliamentarians in time, a hearing via video link could take place in early January.

It had looked on Wednesday as if European conservatives were trying to kick the hearing into the long grass. The European People's party (EPP), the alliance of centre-right parties, had raised a number of concerns about inviting Snowden for a hearing, noting that it could endanger the transatlantic trade agreement with the US.

But on Thursday morning, the leaders of the main political groupings in the European parliament voted to invite Snowden. In the coming weeks, questions will be compiled and then forwarded to the former NSA contractor's lawyer, with roughly two questions coming from each political group.

Labour MEP Claude Moraes, the lead rapporteur for the European parliament inquiry on the mass surveillance of EU citizens, welcomed the outcome of the vote and promised that questioning would be "rigorous and fair".

"Amongst the questions I will ask Mr Snowden," Moraes said, "will be why he decided to reveal the information and the consequences and implications of his actions; questions around his current situation in Russia; questions around his opinion on the impact of his revelations on security, the intelligence services, and 'the right to know'; questions around his opinions of where his revelations and allegations take the area of mass surveillance in the future."

The European parliament hopes to create an interactive situation for the hearing, where MEPs can interview Snowden in real time. However, as there are some concerns that a live linkup might allow the NSA to pinpoint Snowden's location, answers may end up having to be pre-recorded.

The British Conservative party, which is not part of the EPP, had clearly stated its opposition to inviting Snowden at the end of last week.

Conservative MEP Timothy Kirkhope had described the invitation as "a provocative act" which would "endanger public security around Europe and beyond".