Last year, the UK Government began a "balance of competencies review", amounting to an audit of EU powers and their impact on the UK, which could later help provide the basis for the Tory repatriation plan.
Last night, when asked about the details of which powers the Tories wanted to move from Brussels back to London, Foreign Secretary William Hague remained vague. He referred to the party's last manifesto but admitted "circumstances move on".
The 2010 manifesto referred to three areas – the charter of fundamental rights, criminal justice, and social and employment legislation – where powers "should reside with the UK, not the EU".
In October, Home Secretary Theresa May said the UK Government intended to opt out of 130 EU measures on law and order, including the European Arrest Warrant, which the LibDems supported. It could opt back into some later on if the rest of the EU agreed.
In his speech, David Cameron pointed to extending Britain's opt-out from parts of the European working time directive.
He said: "It is neither right nor necessary to claim the integrity of the single market or full membership of the European Union requires the working hours of British hospital doctors to be set in Brussels."
This month, the Fresh Start Group of Tory MPs laid out areas it wanted Britain to retain control over, including financial services, social and employment law, policing and criminal justice.
Just what powers a Tory Government might be able to repatriate after the 2015 General Election is unclear but Nick Clegg, the Deputy Prime Minister, famously said such plans were a "false promise wrapped in a Union Jack".