The second nightmare for the prime minister is the prospect of the Labour party being seriously split over the affair with grass roots activists in London defying his leadership and supporting Mr Livingstone.

BBC: Blair's mayor crisis

Asked about the prospect of a wider referendum at prime minister's questions, Mr Cameron said "we are in Europe and we have to make it work for us".

BBC: Tory MPs seeking Labour dialogue over 'EU overhaul'

Commentators and politicians have offered the prime minister their advice, reflecting on the prospect of a referendum after the next election, the benefits of life inside and outside the EU and divisions within the Conservative Party.

BBC: UK Politics