Some of the billions of pounds handed to farmers every year could be diverted to cash-strapped hospitals after Britain leaves the European Union, Theresa May’s top policy adviser has said.

George Freeman MP, who chairs the Prime Minister’s policy board, said once people realised how much cash was spent on farming subsidies they would want it to be diverted to hospitals, unless ministers made a strong case for how the money was spent.

Mr Freeman was speaking hours before Andrea Leadsom, the Environment secretary, confirmed at the party's annual conference in Birmingham that the Government was committed to keeping farming subsidies at their current level until 2020.

However, with Britain now due to leave the European Union by March 2019, Mr Freeman’s remarks will prompt speculation that farming subsidies - worth £3billion a year - will be cut after Brexit.

Challenged over whether these subsidies would continue after Brexit, Mr Freeman - who was appointed by Mrs May in the summer - said that “in no sector is the shake out from Brexit going to be more profound and there is a lot of negotiating to do”.