Theresa May’s speech today on Brexit may turn out to be every bit as momentous as that of her predecessor four years ago.

On January 25, 2013, David Cameron committed himself to the referendum whose consequences his successor has to deal with. The Prime Minister is expected to put flesh on the bones of a policy that has previously been discernible if not clearly defined.

After months intoning the mantra “Brexit means Brexit”, Mrs May will finally say what it involves, or at least that is what is promised. Suddenly, the exit that seemed so distant when Mr Cameron made his pledge is drawing near.

The process of leaving will begin when Article 50 of the Lisbon Treaty is triggered before the end of March, now just 12 weeks away. The former prime minister never imagined that his promise of a vote would actually lead to the UK’s departure from the EU.

For Mr Cameron, the referendum was as much a device to manage divisions on the Right of British politics as a decision to give the country a say on this matter for the first time since 1975. Mr Cameron’s referendum was predicated upon an assumption that he would achieve reforms of the EU-UK relationship on which he would base his campaign to stay. In the event, he obtained not very much and hardly mentioned the renegotiated package during the referendum. One reason that he got so little was that it was clear to everyone on both sides that he was not prepared to walk away from the negotiating table if the EU offered a poor deal.