Britain is committed to working with the US to destroy the “caliphate” set up by Islamic State militants, the prime minister has said. David Cameron, while speaking about the UK’s possible role in fighting the group to American NBC said: “I want Britain to do more. I’ll always have to take my parliament with me. We’re talking and discussing at the moment, including with the opposition parties in Britain, what more we can do. But be in no doubt, we are committed to working with you to destroy the caliphate in both countries.” Last week Labours interim leader Harriet Harman was invited to a National Security Council briefing on the threat in Syria- which was seen as a further sign of a possible parliamentary vote to extend air strikes in the autumn. But Labour and Lib Dems have called for an explanation in parliament after it emerged that RAF pilots had taken part in bombing raids over Syria despite MPs having approved action against IS only in Iraq. Mr Cameron is expected to give a speech on Monday setting out the government’s future strategy to combat radicalisation and extremism.